Community and Public Health has issued a health warning for the Ashley River at the Rangiora-Loburn Bridge.

The warning follows finding moderate to high cover of potentially toxic algae (benthic cyanobacteria) in the Ashley River at the Rangiora-Loburn Bridge.

People should avoid the area and animals, particularly dogs, should not be allowed near the water until the health warning has been lifted.

People are advised to treat every low-flowing river cautiously, check for the presence of benthic cyanobacteria and avoid contact.

Canterbury Medical Officer of Health Dr Matthew Reid 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.”

“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”, Dr Reid says.

Pets that show signs of illness after coming into contact with algal mats should be taken to a vet immediately.

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.