Canterbury DHB has issued a health warning after potentially toxic algal blooms were found in Selwyn River at Chamberlains Ford, near Christchurch.
The DHB issued a warning after finding “moderate to high cover” of the potentially toxic algae (benthic cyanobacteria) in the river.
People are asked to avoid the area and keep animals, particularly dogs, away from the water until the health warning is lifted.
The algae may also be present along access points of the river.
“People are advised to treat every low-flowing river cautiously, check for the presence of benthic cyanobacteria and avoid contact,” the DHB said.
Dr Cheryl Brunton, Canterbury Medical Officer of Health, said exposure to the algae could cause skin rashes, nausea, stomach cramps and tingling and numbness around the mouth and fingertips.
Brunton said the algae looked like dark brown to black mats and can produce toxins harmful to people and animals.
“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.”
Animals that show signs of illness after coming into contact with the water or the algae should be taken to a vet immediately.
A low cover of the algae can happen naturally, but can increase quickly in warmer months.
Algal blooms are caused by nutrients in the water, sediments and warm, calm weather.
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