Latest updates on the Wastewater Treatment Plant

The latest on the ponds

The wastewater treatment plant is performing reasonably well under the circumstances, and pond conditions have continued to improve. Algae numbers and dissolved oxygen levels are improving, supported by the recent run of settled, sunny weather.

We are still cautious heading into the transition to winter, especially given how challenging summer has been for the pond system. The change in season can create fluctuations in oxygen and biological activity, which in turn can cause spikes in odour.

Overall, we are seeing slow and steady improvement, and things are notably more stable than they were a month ago. While spikes in odour remain possible – particularly overnight or during calm conditions – the general trend has been positive.

The latest pond odour tracker update is now live, with pond 2b moving from red to orange and pond 3 moving from orange to green, reflecting the positive changes in the pond system.

Response to the abatement notice

We submitted our response to Environment Canterbury’s abatement notice yesterday.

The full response includes several documents and components, but the key element relating to odour improvement is a report staff are currently working on, which will go to Council in early April. This report outlines a range of options to reduce odour including:

• Increasing aeration on the oxidation ponds.
• Creating a diversion pipeline to send a portion of treated wastewater directly to the ocean outfall.
• A combination of both increased aeration and a diversion pipeline. 

Another part of the response is an updated Odour Mitigation Plan, which is available now on our website.

Once the Council decides what option to proceed with, we’ll be able to provide more certainty around timeframes, costs, and next steps. In the meantime, work is progressing so that we can move quickly once a decision is made.

Watch the community board update

Our Three Waters Manager, Adam Twose, provided an update to the Waitai Coastal‑Burwood-Linwood Community Board last night. This included an outline of how a diversion pipeline could operate.

Sunny conditions support pond health

Pond conditions have remained stable over the past week, with a slow, steady trend of improvement. Odour levels have generally been low during the day, with some increases overnight when still conditions allow odour to settle and linger.

The recent stretch of sunny weather is helping support pond performance. These brighter conditions are favourable for algae activity, which plays an important role in maintaining oxygen levels across the ponds.

We still believe the ponds are transitioning into their winter‑mode pattern as the temperatures cool. This is when the algae and biological activity in the ponds can become imbalanced, and lead to temporary increases in odour. 

Ocean outfall and mitigation options 

Our team is continuing detailed technical work on options to improve pond health. 

As we've mentioned previously, one of these options is diverting a proportion of treated wastewater around the ponds and directly to the ocean outfall.

Alongside the outfall option, the team is also looking into  aeration at the ponds to boost treatment capacity and overall system performance.

Both of these options are in the planning stage, and no decisions have been made. Before any direction is confirmed, a proposal will go to councillors for consideration and a formal decision.

What to expect over the weekend

With settled conditions at times and the ongoing seasonal transition, intermittent odour remains possible – especially overnight or early in the morning when calmer air allows odour to hang around. During the day, the mild and sunny conditions should continue to support pond stability.

We’ll continue daily management actions and close monitoring through the weekend to respond quickly to any changes.

Tune in to Monday's Community Board update 

At 4.30pm on Monday, Wastewater Treatment Plant Operations Manager Adam Twose will brief the Waitai Coastal‑Burwood‑Linwood Community Board on the option to divert a proportion of treated wastewater directly to the ocean outfall. 

This session is an information update only. No decisions will be made – it’s simply an opportunity to keep the Board and community informed about how it could work and the work underway.

The briefing will be uploaded to the Waitai Community Board YouTube page immediately following the meeting. If you’d like to attend in person, the meeting will be held at the Waitai Community Board room on the corner of Union and Beresford streets.

A word from Gary Watson 

Just a brief update from me this week. I’ve only been back from leave for a few days and have been busy getting back into the swing of things. Even so, I’ve had some really insightful conversations with local community members. Thank you, as always, for your openness and willingness to share your thoughts with me.

I’m looking forward to spending more time out in the community over the next couple of weeks, reconnecting and continuing the conversation. I’ll also be at the board briefing on Monday afternoon.

If you’d like to catch up or chat through anything, feel free to get in touch anytime at Gary.Watson@ccc.govt.nz.

Tuesday 10 March update

Pond condition stable 

Conditions across the ponds have remained stable since last week, with no changes to the odour status tracker. Overall pond health remains fragile – pond 2B is showing some positive response, while ponds 1 and 2A are holding steady but still not in strong condition.

We’re continuing hydrogen peroxide dosing, and the percarbonate trial at the temporary activated sludge plant is ongoing. We used the jetboat late last week and it remains on standby.

With a mixed weather pattern ahead – cooler nights, warmer daytime temperatures, shifting winds, and periods of calm – intermittent odour is possible at times. While we don't expect these conditions to create strong, sustained odour, they can allow odour to linger or move into different areas depending on wind direction and strength, especially as the ponds continue their gradual transition toward winter-mode conditions.

We’ll continue daily management actions and close monitoring to respond quickly to any changes.

Ocean outfall 

Our team continues to investigate the possibility of diverting some treated wastewater to the ocean outfall. There are important steps we need to work through before this plan can progress.

New hydrogen sulphide monitoring dashboard launched

Our new hydrogen sulphide monitoring dashboard shows the hourly averages of hydrogen sulphide measured at each of our five monitors. Just select a location on the map to see the latest H₂S level for that monitor. 

Please note:

This dashboard provides monitoring information to support community awareness. While Christchurch City Council always works to make sure the information is accurate and up to date, data may occasionally be delayed, incomplete, or unavailable due to operational or technical factors. 

The biological health of the ponds is fragile. Spikes of odour are being detected at community monitoring sites. Our teams are doing everything they can to address the current situation.

The long-term fix: Activated sludge reactor construction update

Construction of the new activated sludge reactor is progressing well, and it remains the key long-term solution to odour from the wastewater treatment plant following the fire.

Excavation at the new plant site is now well advanced, and we’ve started sheet piling along the temporary pipeline, as seen in the picture above with the orange digger driving into the ground. As part of this stage, we’ll monitor vibrations throughout the construction and implement mitigation measures where possible to minimise the impact on neighbours. 

The installation of stone columns is also ramping up, with subcontractor setup underway and trials planned for this month. If the trials are successful, we'll start installing those columns in earnest after the Easter break. 

Design work is progressing in parallel, including the development of the new odour treatment system that will operate alongside the reactor once it is complete.

The first set of pipes have been packed up and are on their way to New Zealand.

We’ll continue to share updates as the project moves through its next construction phases, and you can view monthly progress videos on the project webpage.

Friday 6 March update

We’re continuing to see gradual improvements in the ponds. The latest monitoring shows that pond 6 has moved from orange to green on our odour status tracker. This is a good sign and suggests the ponds are very slowly heading in the right direction. The other ponds remain much the same, but overall the trend is slow but steady improvement. Despite this, the pond system remains very susceptible to changes in the weather.

We’re continuing to dose hydrogen peroxide into the ponds, and our trials using percarbonate at the temporary activated sludge plant are still underway.

Our maintenance contractor has been carrying out planned checks on the pond 1 aerators. This meant each aerator needed to be briefly taken offline while the work was done. All aerators are now operating again.

Seasonal change can mean more odour 

In previous years, spikes of odour have occurred as the oxidation ponds transition from summer to winter conditions.

This seasonal change happens as temperatures drop and the natural algae and biological activity in the ponds reduce. If this shift occurs too quickly or becomes unbalanced, it can create low-oxygen conditions that generate odour.

This year, the cooler and wetter summer has meant algae levels have remained lower than usual, so the ponds have effectively been operating closer to “winter mode” for some time already.

While this reduces the likelihood of a sudden transition, our team continues to closely monitor pond performance and proactively manage aeration and treatment processes to minimise any potential odour effects on the surrounding community.

We remain committed to maintaining stable operations and keeping our local residents up to date.

What to expect this weekend 

As we mentioned earlier in the week, the mix of cold weather followed by warmer, settled conditions can make odour more noticeable. When the air is still and temperatures rise after a cold snap, odour can hang around for longer and move into nearby suburbs more easily.

Because of this, there is the potential there could be some increases in odour at times over the weekend even though most of the ponds are stable.

Our team will continue monitoring conditions closely and carrying out the daily actions that support algae and oxygen levels in the ponds.

How diverting treated wastewater to the ocean outfall would work 

We’ve heard a lot of questions about the wastewater pipe that the Council is currently investigating as one option to help reduce the stench from the oxidation ponds. While no decisions have been made, this update explains how the pipe would work, and how it fits in with the existing treatment process.

Why a pipe is being looked at

Diverting a proportion of treated wastewater around the oxidation ponds to the ocean outfall would help ease pressure on the ponds by reducing the volume of treated waste they need to handle.

Since the 2021 fire damaged parts of the wastewater treatment plant, higher loads of waste have been entering the oxidation ponds. This has made it harder for the ponds to maintain healthy oxygen levels, particularly when coupled with unexpected weather conditions. All these factors contribute to ongoing odour issues.

The process 

1.       A portion of the already‑treated wastewater would be diverted around the ponds, rather than through them.
 

2.       Because the ponds normally reduce bacteria, this diverted flow would instead be disinfected with chlorine to ensure it meets consent limits for bacteria.
 

3.       Before entering the ocean outfall pipe, this disinfected flow would be mixed back in with the pond-treated water. 

All wastewater is treated

All wastewater would continue to be treated at the main plant before going anywhere near the pipe. This treatment process includes:

·       Screening to remove larger material

·       Primary sedimentation to settle solids

·       Temporary activated sludge processing to break down organic material

·       Final clarification to remove remaining solids

This treatment happens inside the plant – not in the ponds.

Adding chlorine to reduce bacteria 

Because the ponds normally reduce bacteria, this diverted flow would instead be disinfected with chlorine to ensure it meets consent limits for bacteria. Before entering the ocean outfall pipe, this disinfected flow would be mixed back in with the pond-treated water.

Meeting consent conditions 

If this option progresses any discharge to the outfall would need to meet the consented limits.

On Wednesday, our team had a positive meeting with Environment Canterbury staff to discuss what the consent process would involve if this option is progressed. 

Where is the ocean outfall  

The long outfall pipe discharges three kilometres off New Brighton beach. The total outfall pipe length from the oxidation ponds is 5.2 kilometres and it is 1.8 metres in diameter.  It is buried about eight metres below the sea floor.

When it would be used

If approved, the pipe would be a temporary measure until the new activated sludge plant is built and operational.

Next steps 

There are important steps we need to work through before this plan can progress. We have staff  developing a plan as quickly as possible, and we will keep you updated as this progresses.

Christchurch Wastewater Treatment Plant update

Wednesday 4 March

We know many of you will have questions following the Mayor’s announcement on Monday that we're looking into sending treated wastewater directly to the ocean outfall pipe.

This is one option we are actively investigating, and it is still in the early planning stages. Staff are looking at whether we could divert a proportion of treated wastewater flow so it goes straight to the outfall pipe instead of through the ponds. Reducing the load on the ponds would help lift oxygen levels and ease the conditions that create stench.

There are important steps we need to work through before this plan can progress. We'll continue to update you through this newsletter and on our website. We’ve added a new drop‑down section to the common questions page so you can easily find the latest information related to this option.

Spikes in odour possible

Our latest pond monitoring shows a small improvement in the health of ponds 3 and 4, which have moved from red to orange on our odour status tracker. This is a positive step, and we’ll keep watching these ponds closely over the coming days.

However, the current cold snap could potentially result in an increase in odour. Cold temperatures slow down algae growth, which reduces the natural oxygen in the ponds. The forecast shows warmer and more settled weather. These conditions can cause hydrogen sulphide to linger above the ponds and move into nearby suburbs, so we expect some ups and downs in odour levels.

Our teams are continuing daily actions to support pond recovery, including:

• ongoing hydrogen peroxide dosing to lift oxygen levels
• sodium percarbonate dosing
• close monitoring of water quality and algae health.

Friday Wastewater Treatment Plant update

What to expect this weekend 

The condition of the ponds is much the same as yesterday and we expect spikes of stench will continue over the weekend. These will vary depending on the weather, especially wind direction, and it may affect different areas at different times.

Abatement notice from Environment Canterbury 

We have received an abatement notice from Environment Canterbury in relation to odour from the Christchurch Wastewater Treatment Plant. We have been working closely with Environment Canterbury over recent months, keeping them informed of the steps we are taking to address odour, including through our Odour Mitigation Plan and the daily monitoring and operational improvements underway at the ponds.

In simple terms, the notice states that the plant is currently breaching its resource consent because odour is travelling beyond the boundary of the treatment plant and oxidation ponds. Under the notice, we are required to provide Environment Canterbury with a comprehensive management plan outlining how we will meet consent conditions, including monitoring processes, standard operating procedures, and contingency actions to minimise odour risk. This must be submitted by 16 March.

We take this notice seriously. Addressing odour remains a top priority and we are committed to doing everything we can to reduce impacts on the community. We will continue to keep the community and Environment Canterbury updated as this work progresses.

Learn more about the abatement notice on Environment Canterbury's website.

When we’ll be in touch again

We'll be in touch again via this newsletter on Tuesday. It is likely odour will fluctuate between now and then, and we have teams working at the plant and ponds everyday doing what they can to address the stench. 

Activated sludge reactor piling installation about to start 

We’ve almost finished the process of removing excess soil and other material from the site for the first stage. This has created the platform for installation of the the stone column piles, which will form the foundations of the new activated sludge reactor.

Our work programme over the coming months will involve installation of sheet piles and the stone column piles.

There may be some noise and vibration caused by this work. To try and mitigate the effects of this, we will be closely monitoring the impacts over the next two weeks to see whether any adjustments are needed.  

During the week beginning Monday 2 March, we’ll start installing sheet piles (sections of steel or concrete) to enable ground improvements near the existing plant buildings.

Then in the week beginning Monday 9 March, we will install some test stone column piles in the main area of the work. This work will take approximately three days, during which we will actively monitor the noise and vibration and make adjustments as necessary.

The main ground improvements will start in early April, as we begin installing the remainder of the stone column piles. This work will continue into the winter months.

We're delivering letters to properties neighbouring the plant. These include contact details for the contractor and project manager, who you can get in touch with if you have questions about the work. 

Wastewater Treatment Plant Thursday update

We know these updates can feel repetitive. Many of you are dealing with the stench every day, and we understand that what you really want is for the odour to stop. That is our top priority.

We’re sending regular updates so we can stay in touch, be upfront about what’s happening onsite, and keep you informed about what our teams are doing to improve the ponds.

The odour can come and go, and people experience it differently across the city, so we want you to have up-to-date information as things change. 

The latest on the stench

The ponds are much the same as earlier this week. The first three ponds are still not healthy, and this is showing up in our monitoring, which has recorded spikes in hydrogen sulphide levels.

The weather expected this week isn’t likely to help pond health. Shifts in wind and temperature can make odour levels increase, and we know many of you notice this straight away.

Our team continues to work on the ponds every day and respond as conditions change. We’re also making progress on longer‑term options, and we hope to share more about our next steps soon.

In the short term, we expect the odour will continue. It will vary depending on the weather, especially wind direction, and it may affect different areas at different times. The odour status map remains the same with six ponds at red and two at orange. 

View the odour status map here. 

When we’ll be in touch again

We’ll send a brief update tomorrow to give you an idea of what to expect over the weekend. With pond conditions and the forecast as they are now, we don’t expect things to change much, so it’s likely there will be spikes of odour across the weekend.

A word from Gary  

Thank you to everyone who came to talk with me at the Bromley Fair. It was really helpful to hear directly from residents about how the smell is affecting you, and what information you want from us.

After looking at the data from the door knock, I can see that the numbers we shared included both the people we spoke to in person and the follow‑up letters that were left in mailboxes. 

I’ll now start revisiting the streets where we didn’t manage to speak with people directly, so I can gather more feedback. It’s clear that people are experiencing the odour in different ways, and I want to understand as many views as I can.

This week I’ve been busy setting up meetings with community members, including the local MP, and tomorrow I’ll be meeting with Pegasus Health.

I’m close to securing a part‑time office in the area so I can be more available for drop‑ins, and I’ll soon have a dedicated email address and phone number for this project.

I will be away from Wednesday 4 March to Tuesday 10 March for a wedding, but I’ll catch up on anything that comes through while I’m gone.

In the meantime, you can get in touch with me directly at gary.watson@ccc.govt.nz.

Why it smells more overnight and early in the morning 

People have been asking why the smell can seem strongest overnight or early in the morning.

There are two main reasons:

·         At night the air is still. Hydrogen sulphide is heavier than normal air, so when there is no wind and sun, the gas can settle and build up. When it does move, it moves slowly and can drift into nearby streets and suburbs at a higher concentration.

·         The ponds produce less oxygen at night. The algae in the ponds normally make oxygen during the day, but they stop doing this at night. This means oxygen levels drop overnight, which can make odour worse.

This pattern is normal for oxidation ponds, but with the current conditions it means the spikes of stench overnight and in the morning are more intense.

How the jetboat works

There has been a lot of interest in why we're using a jetboat on the ponds and how it works. We're essentially using the jetboat (below) as a mobile aerator, which means it helps put oxygen back into the water.

It works in a simple way: the boat moves slowly back and forward. As it moves, it churns the water. This movement helps mix in oxygen, which supports the health of the ponds.

Stay updated

We want everyone to be able to stay updated on what's happening at the Christchurch Wastewater Treatment Plant, and we regularly post new information on ccc.govt.nz/wastewaterfire 

You're welcome to send this update to your networks. If you know someone in the community who doesn’t have email or internet access, please print this newsletter off and pass it to them.

If you know of anyone who would like to receive this e-newsletter they can subscribe online. 

Weekend odour spikes

We know many of you noticed spikes of stench across different parts of the city over the weekend. Thank you to everyone who took the time to report what you were experiencing – we understand this is frustrating, and we remain focused on both immediate actions and longer-term solutions.

The heavy rainfall last week has continued to affect overall pond health, and this aligns with the odours picked up both in the community and our monitors, where elevated hydrogen sulphide levels were recorded (see graph further down the newsletter).

We’ve also updated the odour status map to reflect the current conditions, with all but two ponds now sitting in the red category.

What we're doing

Our staff is actively responding to the changing conditions. This includes:

·         Continuing hydrogen peroxide dosing to help lift oxygen levels and support the biological processes within the ponds.

·         Running a sodium percarbonate dosing trial at the temporary activated sludge plant, with staff refining the approach as results come through.

·         Working closely with specialist consultants on longer‑term improvements that will build greater resilience into the pond system.

·         Monitoring key pond health indicators daily so that we can adapt quickly as conditions shift.

While conditions can change quickly – especially after significant rain – our teams remain focused on doing everything they can to stabilise pond health and reduce the likelihood of further odour events.

Avian botulism

We’re also carrying out work to manage avian botulism at the ponds, as we’re seeing some cases in the area. Our staff are working closely with our Parks team to respond quickly and minimise the impact on wildlife.

When we’ll be in touch again

We know odour events are frustrating and affect day‑to‑day life. We want to acknowledge that, and to assure you that improving conditions remains our priority.

We’ll send our next update on Thursday. In the meantime, our teams will continue working hard on site each day to support pond recovery and respond to changes as they happen.

There will likely be fluctuations in odour between now and then. Factors like weather, wind direction, and other environmental conditions can shift quickly, and these can influence how noticeable odour is at different times and in different parts of the city.

Christchurch Wastewater Treatment Plant update Thursday 19 February

This morning's odour 

We know that the odour was particularly noticeable for a period this morning, and this was picked up on some of our odour monitors. We’re sorry for the disruption this may have caused.

While we had taken steps to manage the impact of the recent rainfall event, these situations are unpredictable and we knew some odour was possible. Weather conditions have since improved, and the odour has largely subsided.

Odour levels can change quickly, particularly with shifts in weather and other environmental factors. We are continuing to closely monitor the situation and will keep the community updated as soon as we can if there are any further changes.

When we’ll be in touch again

Unless conditions change significantly, we’ll be back in touch on Monday with another update, including the next round of hydrogen sulphide graphs.

Community outreach – introducing Gary Watson 

My name is Gary Watson, I’m working alongside the local Councillors and Community Board to support good information flow and to look at ways to help make living in the area as positive as it can be while the plant is rebuilt.

I’ve been in community roles at Christchurch City Council since 1999. I delivered the social response in May 2022, meeting many of the affected community over that time.

I intend to be based in your community to be as accessible as possible. It will take me a little time to get things in place, but I will be at the Bromley fair on Saturday cooking the barbeque if you are interested in a chat.

My contact details at this stage are gary.watson@ccc.govt.nz but once I have found a base I will share that address and a phone number with you.

Odour status 

The recent storm and then more settled weather conditions over the last 36 hours have seen an increase in odour from the ponds for a period this morning and a change in our odour assessment, with a higher probability of odour from some of the ponds.

Although Pond 2A has high algae concentration, the results of dissolved oxygen were low and there is low algae concentration in Pond 5 and 6.

Staff are monitoring the odour and making changes where possible. We’re continuing hydrogen peroxide dosing and all of our aerators are operating.

An algal expert has assessed the health of the algae in the ponds and provided a detailed report – read more on that below.

Activity on site

The team is well into excavation for the activated sludge reactor – we have excavated 3200m3 of sand, enough to build about 1 million medium-sized sandcastles. Next week, they will start installing sheet piling to support the existing structure and enable the excavation next to it.

Here’s what you need to know about noise, dust and traffic management:

·       Noise and vibration is monitored at the site boundary, with strict limits in place. If these limits are exceeded, mitigation measures will be put in place.

·       Dust control includes visual monitoring, water carts, speed limits, and other suppression techniques to keep dust to a minimum.

·       Traffic management is in place to reduce impacts on the community. 

Work hours will be Monday to Saturday, 7.30am to 6pm. If any work needs to happen outside these hours, we'll notify the community in advance. 

Algae expert on the ground

An algae specialist visited the ponds last week to help us understand how the ponds are recovering. Algae are a key indicator of pond health – different types show up as conditions improve, so looking at what’s growing helps us track how each pond is doing.

Overall, the specialist found that all seven ponds look healthier than they did in early February when the stench was at its worst. We’re now seeing more of the “good” algae that usually appear in well‑functioning ponds. These early algae help improve the water so more species can return over time.

Pond 1 is still the least healthy, with fewer algae types and more bacteria than we want to see. But even there, we’re starting to notice small signs of improvement.

The other ponds showed good progress, with a mix of healthy green algae and, in some ponds, tiny invertebrates. These are normal in ponds that have good oxygen levels and are treating wastewater well.

We’ll keep checking algae regularly. It’s one of the key tools helping us understand how the ponds are recovering and what to expect as conditions continue to improve.

Where we're at:

It was a positive weekend at the plant, with continued signs of improvement across the ponds. Dissolved oxygen levels and algae recovery have both trended upward, and odour levels have eased noticeably over the past two days. The weather has played a big part in helping stabilise pond conditions.

We know some of you will have been dealing with the Boil Water Notice for the Rawhiti water supply zone. This notice has now been lifted for everyone, except approximately 20 properties who will need to keep boiling their water. We will be communicating with these residents directly. You can find more information on our website.

Aerator update – Pond 2A

One of the new aerators on Pond 2A stopped operating on Sunday. Our operations team has prioritised this and is working on repairs. We will return it to service as quickly and safely as possible to maintain momentum in pond recovery.

Planning for the long-term

Staff are actively working with our specialist consultant on the longer-term resilience plan for the ponds. This work is progressing and focuses on ensuring sustained performance, robustness, and better response capability during challenging conditions.

Upcoming rain event and potential pond impacts

As you know, cooler weather and rainfall can influence how the pond biology behaves. Our team has been watching the forecasts closely and is planning ahead to manage the ponds through this weather event.

With algae and dissolved oxygen levels now heading in the right direction, we’ll be doing everything we can to maintain these gains and protect the progress made over the past several days. Staff will be onsite monitoring conditions throughout the rain.

Community outreach – next steps

Thank you again to everyone who spoke with us during our neighbourhood visits last week. Your feedback has been incredibly valuable and is directly shaping the next phase of support options. We expect to be able to share more later this week about the next steps.

When we’ll be in touch again

Unless conditions change significantly, we’ll be back in touch on Thursday with another update, including the next round of hydrogen sulphide graphs.

End of week wrap up

We want to again acknowledge and apologise for the continued impact the stench is having on the community. We know how tough this has been, and we remain genuinely grateful for your patience.

Our neighbourhood visits earlier in the week were incredibly insightful. Thank you to everyone who took the time to speak with us. Your honesty and thoughtful feedback are helping shape a set of community support options, which we’re now developing further. These will be presented to the elected Council for consideration and approval.

We’ll be back in touch via this newsletter on Monday 16 February, unless something significant changes over the weekend. In the meantime, please know that staff will be on site throughout the weekend, closely monitoring the ponds and doing everything they can to keep the plant operating with as little odour as possible.

Odour status, pond health and acitvity on site 

Since Monday we have seen encouraging improvement across a number of ponds, with ponds 1, 2A and 2B gradually improving. Algae levels and dissolved oxygen have continued slowly trending upward. However, we’re still experiencing spikes in odour, so we’re taking a cautious approach while closely tracking changes.

All aerators are operating on the ponds, and a jet boat was deployed yesterday to boost aeration. A pond management specialist has been onsite having productive, detailed discussions with our plant teams.

We’ve also had crews hard at work on the activated sludge reactor – steadily excavating the trickling filter site, identifying and removing old services, and preparing the area for the next stage of construction.

The pond tracker has been updated reflecting the gradual improvement we’re seeing, particularly across the healthier ponds. We’ll continue to update the tracker as conditions evolve.

We're developing a pond management plan

A pond management specialist is on site with our team today and tomorrow to help develop a new, comprehensive pond management plan. This plan will focus on tracking key indicators – such as algae levels, dissolved oxygen, and other early‑warning signs – as well as making some recommendations so we can act sooner when conditions begin to deteriorate.

The aim is simple – reduce the chance of odour by identifying issues earlier, responding faster, and keeping the community better informed.

We want to reassure you that we’ve already been extensively monitoring these key pond indicators. The new pond management plan builds on this work by strengthening our approach – setting clearer trigger points for when conditions start to shift and outlining earlier, more decisive actions we can take.

Pond system slowly stabilising 

Conditions at the ponds continue to trend in the right direction, with both algae levels and dissolved oxygen slowly increasing. These are positive signs that the system is stabilising, but health indicators in ponds 1, 2A and 2B are still lower than ideal and we continue to monitor them closely. 

Pond condition stable

Conditions at the ponds remain much the same today. Algae numbers are slowly increasing, which is an encouraging sign and an important part of the recovery process. However, there is still odour coming from the ponds, and Pond 1 continues to struggle.

Alongside our immediate work to support recovery, we’re also looking ahead to what can be done in the long term to reduce the chance of another odour event in the future. This work needs to be robust and sustainable, and while it will take a little time to finalise, it remains a high priority and is being fast-tracked wherever possible.

Our teams are working incredibly hard – both to get the ponds healthy now and to take on board the lessons that will help us improve moving forward.

Actions underway 

• A batch of sodium percarbonate has been delivered to site for trial use. Staff are preparing systems to enable dosing to the temporary activated sludge plant as required to improve oxygen levels and support plant performance.
• We've been dosing the ponds with hydrogen peroxide and additional product has been ordered and will be delivered to site.
• Three new aerators installed on Ponds 2A and 2B are fully operational. Staff are closely monitoring performance, particularly in relation to potential odour generation from the new aerator installed on Pond 2B earlier this week.
• A specialist wastewater pond expert has been engaged and will be on site this Thursday and Friday to support the development of a comprehensive pond management plan.
• The jet boat has again been deployed today to provide additional oxygenation to the ponds.

There is no change to the odour status map today. We’ll continue to provide updates as the situation evolves.

Activated sludge reactor update – all go on site!

Work on site is progressing well, and excavation is now in full swing. Crews are steadily removing soil from the site, with the average depth reaching about two metres below ground. This will create the platform needed for installing the stone columns later on.

Next week, the team will move closer to the plant to carry out some exploratory work. This includes locating any existing services that may still be in the ground from the old trickling filter and removing what’s no longer needed. Doing this will allow us to install sheet piling and safely excavate along the temporary bypass line that was put in after the fire.

For the next few weeks, the focus will be much the same – dig, dig, and more digging – as we continue preparing the site for the next stages of construction.

The overall programme is expected to span about three years, with commissioning targeted for 2028. Importantly, we’re able to build the new activated sludge reactor with minimal disruption to current operations.

Wednesday update

Thank you 

We want to start with a thank you to all the residents we spoke with during yesterday’s neighbourhood visits. The kindness, openness, and understanding we received at your doors meant a great deal to our team. We know the stench has been challenging, and we truly appreciate the time people took to talk with us.

Our team visited 750 homes and received 545 responses. For those who weren’t home, we left a calling card with our contact details. If you’d like to speak with us, please give us a ring and leave your name and phone number – we’ll happily arrange a time to call you back.

A clear message came through in our conversations: you want this issue resolved as quickly as possible, and we hear you. These visits were an important step in listening directly to the community, and we’re committed to doing more of this – spending real time with people, answering questions, and hearing concerns firsthand.

We’re now reviewing all the feedback gathered yesterday and developing a set of potential community support options. These will be presented to the elected Council for consideration and approval.

More updates to come as this work progresses – thank you again for your time, your honesty, and your continued patience.

Tuesday update

Our team carried out its usual assessment of the ponds today, supported by drone imagery taken on site. The overall condition of the pond system remains similar to yesterday. We are still seeing lower-than-ideal dissolved oxygen levels in places, especially in the early morning. This means there is an ongoing risk of odour.

However, the warmer, sunnier conditions are helping to support our algae activity across the pond system and we are seeing some really encouraging dissolved oxygen levels during the day. 

New aerator installed in Pond 2B

A new aerator was successfully installed in Pond 2B this morning and is now operating (shown above). This additional aeration will support the pond’s recovery and help reduce the likelihood of odour as the system stabilises.

As with any new aerator, there was the possibility of short‑term disturbance of the sludge layer as it started up. This was not detected during monitoring and we believe that the risk of an increase in odour related to this has now passed. 

Neighbourhood visits 

Around 32 Council staff have been out today visiting roughly 750 neighbouring households to hear directly from residents about their priorities.

If no one was home, staff will have left contact details so people can still get in touch. The information collected will help inform possible options for community support, noting that any decisions would need to be made by the elected Council.

Monday update

We’re continuing to closely monitor the health of the ponds, with daily checks. Today, we can report that the health of the ponds is continuing to recover, but dissolved oxygen levels remain at lower than ideal, which means there is a risk of increased odour.

A new aerator for Pond 2B is being installed and tested today, and we’re hoping to have this up and running tomorrow. When the aerator is switched on, it will temporarily disturb the sludge, which may produce a localised, short‑term odour lasting 1–3 hours. We’ll be using our odour monitoring equipment to assess how much odour is being generated and respond accordingly to minimise odours.

Our community odour monitoring sites are being updated more frequently, and we’re monitoring the weather, with rain expected later in the week. We’ve sent an algae sample to a specialist lab, which has confirmed that the species appearing in high numbers is consistent with ponds under heavy load. Our team is now working with experts to put together a plan that will help make the ponds more resilient in the future. 

What happens next

About 32 Council staff from across the organisation will be calling on the immediate neighbours of the Wastewater Treatment Plant (around 750 homes) tomorrow (Tuesday) to hear the community’s priorities. If they’re not home, we’ll leave contact information so they can get in touch.

The information will be collated and provide valuable insight into the possible options for community support. Any decisions would need to be made by the elected Council.

Waitangi Day weekend update

We've kept a close eye on the pond health over the last couple of days, and nice weather has seen their condition improve – especially Pond 2B (above), which we've been able to downgrade from 'High' to 'Possible' odour status. See the odour status map here. We've dialed back the hydrogen peroxide dosing for now.

Unless the odour gets unexpectedly bad before then, we'll be in touch again on Monday. The team will continue working through the long weekend, and we're still on track to install the new aerator for Pond 2B early next week. As mentioned, we're also working to get our community odour monitoring dashboard online.

Thursday update

The latest

The team will work all through the long weekend to keep the plant running effectively and keep any odour to a minimum. Today, we can report that the health of the ponds is still showing signs of improvement – we're reviewing the preliminary algae report, dosing the ponds with hydrogen peroxide, and fast-tracking the installation of a new aerator for Pond 2B for early next week. We'll keep a close eye on the weather, and how much odour is being generated, as we get it up and running.

In the background, we're also working to get our community odour monitoring dashboard online. We're also seeing improvement in the level of hydrogen sulphide.

Odour mitigation plan

We've just approved our step-by-step plan to mitigate the odour and you can read it here.

Updates over Waitangi weekend

With decent weather in the forecast for the long weekend, we're cautiously optimistic the situation at the plant will continue to improve. Our next update will be on Saturday afternoon, unless there's a sudden change of status at the plant, in which case we'll share updates as soon as we can.

Sludge reactor progress

We've confirmed the timeline for construction of the new activated sludge reactor – the earthworks have already started. Once it's up and running, the new reactor will fix the odour issues. You can see our plans on the timeline at the bottom of this page.

Pond conditions continue to improve

We’ve been out on site again today and are pleased to report further improvements across the pond system with odour levels dropping.

Following yesterday’s rain, flows through the ponds have increased, and we’re seeing positive changes in the pond colour, which is shifting back toward a healthier state. There is also a noticeable amount of algae returning around the edges of Pond 2, which is an encouraging sign of recovery. All aerators are operating as they should.

Looking ahead, the expected sunny conditions should support the continued return of algae and help the ponds regain their natural balance.

While staff are cautiously optimistic about recent improvements in pond health, the ponds remain in a delicate and changeable state. Current odour monitoring is showing low levels of odour, however, under certain weather and operating conditions there remains a risk of odour returning.

We're meeting with external experts tomorrow to identify ways to strengthen the future resilience of the pond system and reduce the risk of similar events happening again.

Recap – Residents meeting

Last night’s community meeting in Bromley was well attended. Thank you to everyone who came along.

We want to again acknowledge the hardship the community has faced and the impact the ongoing stench has had on daily life - not only in recent weeks, but throughout the years since the fire. We are committed to improving our processes so we can reduce the risk of similar events happening again, and provide earlier warnings when conditions change in the future.

The Mayor and Council staff gave an update on how this situation arose. We also heard clearly the call for better engagement. Your feedback is guiding our next steps.

Come and see us tomorrow

We'll have staff on the corners of Carters and Shortland streets tomorrow. Look out for the Council-branded trailer and feel free to come and speak one-on-one with members of our Community Partnerships and Three Waters teams. 

Door knocking next week 

Next week, we'll be in the community visiting neighbours of the plant to hear from them directly about their priorities. 

If you couldn't attend the meeting, watch the video here. 

Ponds showing signs of improvement

Our latest monitoring suggests signs of improvement. The pond system is looking healthier today, and we’re optimistic that things are moving in the right direction.

Overnight we adjusted pond flows in anticipation of the predicted rain, and we’ll continue making operational changes as needed to manage the weather conditions and support the recovery of the ponds. 

Our early investigations indicate that the stench is likely the result of a combination of weather factors and wastewater loads into the ponds. Right now our focus is firmly on restoring the health of the pond system. Once things have stabilised, we’ll undertake more detailed investigations to confirm the root cause.

Long-term solution 

Once commissioned, the new activated sludge reactor will address the long‑standing odour issues that followed the fire. We're actively looking for opportunities to accelerate this programme wherever possible, though the timeline is already extremely tight. We’ll continue to make the most of any chance to bring that work forward.

Our contrators are already busy getting construction started and the programme is expected to take about three years, with commissioning targeted for 2028. 

We know this is a long time to wait, and while we construct the new plant we're doing everything we can to keep the fire-damaged plant and oxidation ponds operating as well as they can. 

Poor conditions starting to stabilise

As you know, over the past few weeks we’ve experienced significant challenges with the Christchurch Wastewater Treatment Plant's oxidation ponds – unexpectedly, conditions are the worst they've been since the fire.

Usually at this time of year the ponds are very healthy, but several compounding factors have contributed to the stench.

How we got here

Each year, the wastewater load which arrives over the holiday period varies significantly as industry shuts down for the summer holiday and our population varies. The temporary activated sludge plant, which is a biological process, doesn't manage this variation very well.

This can result in the temporary plant struggling and passing additional load to the ponds, however usually at this time of year the ponds are very healthy and are able to pick up the slack.

On top of this, we expected the high levels of rain in January to help flush wastewater through the system and improve pond health – however, this didn't happen, as it appears to have set back the algae growth in the ponds.  

While we know the weather and high load are contributing factors, our team is reviewing all data to understand whether other factors also played a role in the current situation.

We’ve always known we're operating the temporary plant with a narrow margin for error, as it has no extra capacity. This makes the system more vulnerable to sudden changes. While the ponds are now showing signs of improvement, much of the recovery depends on natural processes such as algae growth and oxygenation.

Despite these challenges, we're using every tool available and are seeing progress. Increasing aeration in the ponds remains a key focus.

What we’re doing

• Balancing flow between ponds to better distribute load and support recovery.
• Regular jetboat oxygenation to increase dissolved oxygen.
• Ongoing monitoring of key pond health indicators, including dissolved oxygen levels, drone imagery, and lab samples (with a focus on algae levels, a major oxygen source).
• Updating our odour mitigation plan to reflect the current event.
• Doubling our odour assessment frequency, with an external contractor now reporting twice weekly (these graphs will be updated to our website).
• Dosing the ponds with hydrogen peroxide to support pond oxygenation.
• Monitoring the weather ahead of the incoming cold, wet system to help determine the best way to manage flows through the ponds.

Health, wellbeing and support services 

We’re sorry for the impact this continues to have on you and your whānau. Please be assured we are doing everything we can to support the system’s recovery and reduce odour where possible.

Dr Annabel Begg, Medical Officer of Health for the National Public Health Service has provided the advice below:

"Exposure to hydrogen sulphide odour arising from the Christchurch wastewater treatment plant can cause nausea, headaches, eye and throat irritation, skin irritation, sleep disturbance, and worsening asthma symptoms at relatively low concentrations.

"If people exposed to the odour don't experience physical health effects, continued exposure to unpleasant or nasty, noxious odours can still have an adverse effect on people's mental wellbeing.

"While exposure to hydrogen sulphide is unpleasant and may result in health effects, it doesn’t accumulate in the body. Any health effects would be expected to resolve when the odours are brought back to normal levels, and long-term health effects are highly unlikely.

"People experiencing health issues as a result of the odour coming from the treatment plant should seek health advice from their GP, doctor, Hauora or healthcare provider, or call Healthline free on 0800 611 116, anytime 24/7 for advice as soon as possible. In an emergency call 111."

There are also free services across Ōtautahi Christchurch available to support and enhance overall health and wellbeing. These include:

Health Improvement Practitioners (HIPs)

HIPs are qualified mental health professionals based in General Practices (GPs). They offer free, 15–30 minute sessions focused on practical strategies to support mental and physical wellbeing. There is no limit to the number of sessions you can access.

You can book directly through your GP.

Pae Ora ki Waitaha Support

Pae Ora ki Waitaha is a free healthy lifestyles service developed with Māori and Pasifika providers.

More information is available on their website. 

Healthline

Healthline is a free over-the-phone health service available 24 hours a day, seven days a week. If you or someone in your family is unwell, you can call Healthline and speak to experienced nurses and paramedics for health advice and information about what to do next.  

Call 0800 611 116.

Other options we’re considering

·       Methods to boost oxygen in the temporary activated sludge plant.

·       Specialist algae sampling to help us further understand the situation.  

What to expect

The dissolved oxygen levels have stabilised and are beginning to improve. While algae numbers remain low, results confirm algae is present in Ponds 1, 2A and 2B, with encouraging rebounds in Ponds 4, 5 and 6. The pond colour is also changing, which is another sign that conditions are starting to turn.

We remain focused on stabilising and improving the ponds before conducting a full review to identify any additional triggers behind this event.

Stay updated

We want everyone to be able to stay updated on what's happening at the Christchurch Wastewater Treatment Plant, and we regularly post new information on ccc.govt.nz/wastewaterfire 

You're welcome to send this update to your networks. If you know someone in the community who doesn’t have email or internet access, please print this newsletter off and pass it to them.

If you know of anyone who would like to receive this e-newsletter they can subscribe online. 

If you have any questions, or would like further information on the project, please call us on 03 941 8999 or 0800 800 169 or email wastewater@ccc.govt.nz  

Thanks for your patience and understanding. We’ll be in touch again soon.

Positive signs with recent weather

Our teams have been onsite throughout the weekend closely monitoring pond conditions, odour levels and system performance. At this stage, pond conditions remain largely unchanged since our last update. Dissolved oxygen levels are still low across much of the system, so the stench is likely to continue in the short term.

The recent stretch of sunshine is helpful. Warm, bright conditions support algae growth, which plays an important role in restoring dissolved oxygen in the ponds. As algae activity increases, we expect this to gradually improve pond health. While this won’t deliver an immediate change, it is a positive factor supporting ongoing recovery.

What we’re doing

Our staff continue to:

• Monitor pond health and odour in real time.
• Review results and make small, controlled adjustments to support system stability.
• Keep aeration equipment and flow diversions operating as effectively as possible.

We know the stench is unpleasant and disruptive, and we’re sorry for the impact this continues to have on you and your whānau. Please be assured we are doing everything we can to support the system’s recovery and reduce odour where possible.

There are free services across Ōtautahi Christchurch available to support and enhance overall health and wellbeing. These include:

Health Improvement Practitioners are qualified mental health professionals based in General Practices (GPs). They offer free, 15–30 minute sessions focused on practical strategies to support mental and physical wellbeing. There is no limit to the number of sessions you can access.

You can book directly through your GP.

Pae Ora ki Waitaha is a free healthy lifestyles service developed with Māori and Pasifika providers – www.waitaha.health.nz/health-professionals/pae-ora/

Healthline is a free over-the-phone health service available 24 hours a day, seven days a week. If you or someone in your family is unwell, you can call Healthline and speak to experienced nurses and paramedics for health advice and information about what to do next. Call 0800 611 116.

We want everyone to be able to stay updated on what's happening at the Christchurch Wastewater Treatment Plant, and we regularly post new information on ccc.govt.nz/wastewaterfire

View the full newsletter here: https://createsend.com/t/r-CC104E14CC4A84162540EF23F30FEDED and subscribe to receive this newsletter online here: https://confirmsubscription.com/h/r/822D5D6D9FECF8772540EF23F30FEDED

What to expect over the weekend

Our staff are onsite monitoring the situation in real time, taking action to stabilise the ponds, and working to minimise odour where possible. Odour is likely to continue for now, but we are doing everything we can to manage and reduce its impact.

We know the odour is frustrating and unpleasant, especially for residents living close to the plant. We want to reassure you that our staff are working hard to manage the situation.

A recap on what's causing the odour

The recent heavy rainfall has disrupted the biological processes within the oxidation ponds. Monitoring shows dissolved oxygen levels have dropped across the system. Low‑oxygen conditions make odour more likely, especially in Ponds 1, 2 and 3, which are currently the most affected.

In past wet‑weather events, additional rainfall has supported pond recovery. This time, the ponds have not responded in the usual way. Increased inflow and load into the system have added further pressure, increasing the likelihood of odour.

We know the smell is unpleasant and disruptive, and we are sorry for the impact this is having on you and your whānau.

What we’re doing

• We’re monitoring pond health and odour continuously across the plant and in the surrounding community. Staff are reviewing results and making adjustments where possible. Recent and ongoing actions include:
• Actively monitoring the temporary activated sludge system, which is performing as well as it can under current conditions.
• Adjusting flows through the oxidation ponds to reduce load and odour pressure on the most affected areas, including redirecting more flow from Pond 1 into Pond 4 to take pressure off Ponds 2A and 2B. We’re monitoring this diversion closely while gradually lowering pond water levels to improve flushing and refresh the system.
• Deploying a jet boat on Ponds 2A and 2B to introduce additional oxygen without disturbing settled sludge.
• We recently installed two new aerators on Pond 2, which are performing well, and we’re installing another aerator in mid-February to further support pond health.
• We also continue a range of monitoring including pond sludge surveys, external odour specialist reviews, checking dissolved oxygen levels, upcoming weather conditions and a range of other influencing factors.

We are carefully managing all adjustments to avoid unintended impacts from changing too many factors at once.

What to expect over the weekend

Dissolved oxygen levels across the ponds remain low as of this morning. This means odour is likely to continue in the short term. Conditions may fluctuate depending on weather, temperature and system recovery. We will continue to monitor the situation closely and take further actions as needed.

We want everyone to be able to stay updated on what's happening at the Christchurch Wastewater Treatment Plant, and we regularly post new information on ccc.govt.nz/wastewaterfire

View the full newsletter here: https://createsend.com/t/r-57E575C0BB5288DF2540EF23F30FEDED and subscribe to receive this newsletter online here: https://confirmsubscription.com/h/r/822D5D6D9FECF8772540EF23F30FEDED

What we're doing to monitor and respond to odour

We know the increase in odour is unpleasant and our teams are working hard to manage the situation. There hasn't been a significant change in the situation since yesterday and we're expecting odour will continue for at least the next week.

Our operations team is actively tracking odour at multiple points across the plant and surrounding community, using our odour monitoring tools. Staff are reviewing results in real time and making adjustments where possible to minimise impacts.

Here are some of they key actions we're taking:

Temporary Activated Sludge Plant

• Our temporary activated sludge system is performing as well as it can under current conditions and we've maintained treatment capacity.

Pond flow adjustments

• We’re adjusting flow through the oxidation ponds to reduce load and pressure on the section struggling most with odour.
• Pond water levels will be temporarily lowered to allow more effective flushing and to help refresh the system.

Oxygenation

• Regular monitoring of dissolved oxygen levels continues.
• We'll deploy a jet boat to introduce additional oxygen into the ponds where it can be effective; this will be carefully balanced to avoid inadvertently stirring up settled sludge.

Aerator maintenance and upgrades

• One of the 17 aerators on Pond 1 failed during routine electrical maintenance. Our contractor is working hard to get it returned to service as quickly as possible.
• The two newer aerators installed on Pond 2 in recent months are performing well.
• An additional aerator is scheduled to be installed in February to further support pond health.

If you’re concerned about the impacts of the odour there is a range of information on our website about odour and health, and what support is available for impacted residents.

Stay updated on what's happening at the Christchurch Wastewater Treatment Plant, and we regularly post new information on ccc.govt.nz/wastewaterfire

Heavy rain causing odour

The recent period of heavy rain has significantly affected the health of several oxidation ponds at the Wastewater Treatment Plant which is causing the increased odour we’re noticing.

During previous wet weather events, the additional rainfall has generally supported pond recovery, improving overall pond health and preventing odour issues. However, this time the ponds have not responded in the same way.

Our staff are continuing to collect and analyse data to understand why these conditions have developed on this occasion.

We’ve also seen increased loading to the ponds, which also put more pressure on the ponds, increasing the likelihood of odour.

Our operations teams are working hard to closely monitor conditions and respond wherever possible to improve pond health and minimise odour. This includes:
• Adjusting flows through the ponds to stabilise loading
• Regular monitoring so we can react quickly to changes
• Using all available operational tools to support oxygen levels and improve pond performance

Based on current pond health, we expect higher than normal odour levels may continue for at least the next week. We’ll keep providing updates as conditions change.

We know odour impacts are disruptive, and we want to reassure our community that reducing them is a priority for us.

Find out more: ccc.govt.nz/services/water-and-drainage/wastewater/treatment-plants/christchurch-wastewater-treatment-plant/news-updates-and-meetings

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