Health & wellbeing  |  16 Jan 2019

People and animals, particularly dogs, are being warned to avoid the area of the Waimakariri River near State Highway 1 and Main North Road bridges because of a potentially toxic algal bloom.

Canterbury District Health Board’s Community and Public Health unit have issued a health warning after finding benthic cyanobacteria, a potentially toxic blue-green algae, in the Otukaikino/Waimakariri confluence.

Cyanobacteria in a river.

Cyanobacteria appears as dark brown/black mats attached to rocks along the riverbed.

Dr Ramon Pink, 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 Pink 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.”

“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 therefore should not be consumed,” Dr Pink says.

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

People and animals should remain out of the waterways until the warnings have been lifted.

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

“The phormidium is growing where nutrient rich water from the Otukaikino is running across the cobbled bed of the Waimakariri and slowly mixing with the low nutrient water of the Waimakariri. We expect it will clear when there is a substantial flow in the Waimakariri,” says Dr Tim Davie, Enviornment Canterbury’s Chief Scientist.

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.

View Environment Canterbury's toxic algae video to know what to look for.