The Community and Public Health division of the Canterbury District Health Board have issued a health warning for the Hurunui River at State Highway 7.
The warning follows the finding of high levels of the potentially toxic benthic cyanobacteria Phormidium in the Hurunui River.
People and animals, particularly dogs, should avoid the area of the Hurunui River until the health warning has been lifted. Phormidium mats have been found to be detaching and accumulating at the sides of the River, as well as floating towards the swimming hole site which is located upstream of the SH 7 bridge behind the Balmoral campground. The swimming hole should not be used until further notice.
Dr Alistair Humphrey, 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 water from the river at any time.
Pets that show signs of illness after coming into contact with algal mats should be taken to a vet immediately.
Dr Humphrey says 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.
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