Algal Bloom in Selwyn Waikirikiri River at Glentunnel

Thursday December 22, 2016

​The Community and Public Health division of Canterbury District Health Board have issued a health warning after potentially toxic algae (benthic cyanobacteria) were found in Waikirikiri/Selwyn River at Glentunnel.

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

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 have come into contact with potentially contaminated water and are experiencing any of these symptoms, visit your doctor immediately. Let your doctor know if you've had contact with dark brown/black algal mats or water in this area."

The Selwyn District Council, as the drinking water supplier for the area, are following agreed procedures to ensure their reticulated drinking water supplies are safe.

"No-one should drink the water directly from the river at any time. Even boiling river water does not remove the toxin, and so it 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 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 and the algal mats

  • 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.

For further information visit

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


For more information contact Canterbury DHB Communications Teamleader Mick O'Donnell on, 027 261 4824, or at mick.o'

Page last reviewed: 23 December 2016
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