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Last modified: 29 Jul 2020 10:23am

Canterbury District Health Board’s Community and Public Health unit has issued a health warning after potentially toxic blue-green algae (benthic cyanobacteria) were found in Selwyn/Waikirikiri River downstream of the Glentunnel swimming hole.

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

There are also other access points along the Selwyn/Waikirikiri River that may have cyanobacteria present and people are advised to check for the presence of cyanobacteria and avoid contact.

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.”

The Selwyn District Council as the drinking water supplier are following agreed procedures and monitoring their nearby drinking water intakes.

“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 Humphrey 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
  • 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:

Environment Canterbury - Swimming Water Quality

CDHB - Recreational Water

LAWA - Can I swim here?

For more information on Mahinga kai:

Mahinga Kai