Algal Bloom health warning


Toxic algae has been found at the confluence of the Waimakariri South branch/Otukaikino Stream and the Waimakariri River near the SH1 and Main North Road bridges.

The Community and Public Health team from Canterbury District Health Board has issued a health warning for the potentially toxic blue-green algae (benthic cyanobacteria).

People and animals, particularly dogs, should avoid the area of the Waimakariri River near SH1 and Main North Road bridges until the health warning has been lifted.

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.”

No-one should drink the water from the river at any time, because boiling the water from the river does not remove the toxin.

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:

It 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.

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