26 Jan 2018

Share this story

People are being urged to stay away from the Selwyn/Waikirikiri River near Chamberlains Ford because of a potentially toxic blue-green algae (benthic cyanobacteria).

Dr Alistair Humphrey, Canterbury Medical Officer of Health, says the algae look like dark brown to black mats and can produce toxins harmful to people and animals.

“Exposure may cause skin rashes, nausea, stomach cramps, tingling and numbness around the mouth and fingertips,” Dr Humphrey says.

“If you experience any of these symptoms, visit your doctor immediately, also let your doctor know if you’ve had contact with dark brown/black algal mats or water in this area.”

Pets that show signs of illness after coming into contact with algal mats should be taken to a vet immediately.

Dr Humphrey says people and animals should remain out of the waterways until the warnings have been lifted.

Environment Canterbury is monitoring the sites and the public will be advised of any changes in water quality.

Facts about cyanobacteria:

  • Appears as dark brown/black mats attached to rocks along the riverbed.
  • The algae occur naturally but can increase rapidly during warmer months.
  • It often has a strong musty smell and algal toxin concentrations can vary over short periods with changing environmental conditions.
  • Although high river levels will remove the algal bloom, detached mats can accumulate along the shore and increase the risk of exposure to toxins.
  • If a health warning is in place avoid contact with the water.
  • Although district or city councils may place warning signs, these may not be seen at the numerous river access points, hence the need for people/ dog-walkers to treat every low-flowing river cautiously.