The Community and Public Health division of the Canterbury District Health Board have toxic algaeissued a health warning for Coes Ford.

The warning follows finding high levels of potentially toxic blue-green algae (benthic cyanobacteria) in the Selwyn/Waikirikiri River.

People and animals, particularly dogs, should avoid the area of the Selwyn River at Coes Ford until the health warning has been lifted.

Dr Alistair Humphrey, Canterbury Medical Officer of Health, says the algae looks 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.”

Reticulated town water supplies are currently safe but no one should drink the water from the river at any time.

“Even after boiling the water from the river, it does not remove the toxin and therefore should not be consumed,” Dr Humphrey says.

“Pets should be taken to a vet immediately if they are showing signs of illness after coming into contact with algal mats.”

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.

Further information is available on Environment Canterbury’s website.

Or contact Community and Public Health on (03) 364 1777.