Invasive weeds clogging the Heathcote River and taking over its banks are being targeted in a spring-time weed spraying programme.

The weeds are colonising the riverbanks and will eventually crowd out native species. Some are also growing out into the waterway, restricting flood flows and accelerating sedimentation.

“The weeds are starting to impact on the river’s ecosystem and capacity so they need to be removed,’’ says Christchurch City Council Land Drainage Manager Keith Davison.

“We have bank stabilisation and planting work happening along the Heathcote River as part of our flood mitigation programme in the area and we need to get rid of the weeds before we progress this work any further.’’

The chemical herbicide glyphosate will be used to target the weeds.

“The Council has been trying to reduce its use of glyphosate and in our parks and reserves we are using organic fatty acid alternatives to combat weeds.

“Unfortunately, the organic fatty acid alternatives that are available are not safe to use around waterways because of their toxicity to aquatic invertebrates,’’ Mr Davison says.

“We can’t physically remove all the weeds in and along the Heathcote River so our best option is to use glyphosate, which becomes inactive in soil and sediment, so safe to use around water.’’

Mr Davison says the contractors will follow strict protocols when spraying with glyphosate to minimise the impact on the surrounding environment and to avoid the risk to people travelling through the area.

“The areas that have been sprayed will be clearly marked with warning tape and signage to keep people and their dogs out until the spray has dried.’’

The weed spraying programme is due to start late October, but the work is weather and tide dependent.