Canterbury DHB’s Community and Public Health unit has issued a health warning after potentially toxic blue-green algae (planktonic cyanobacteria) was found in Lake Clearwater, situated in the Ashburton Lakes Basin area.

The type of cyanobacteria currently present in high concentrations is Synechocystis.

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

Dr Ramon Pink Canterbury Medical Officer of Health, says the algal bloom can produce toxins harmful to humans and animals.

“People should avoid contact with the water until further notice.

“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 and please let your doctor know if you have had contact with the lake water,” Dr Pink says.

No one should drink the water from the lake at any time. Boiling the water does not remove the toxin.

Animals that show signs of illness after coming into contact with the water or algal scums should be taken to a vet immediately.

Fish and shellfish can concentrate toxins and their consumption should be avoided. If fish are eaten, remove the gut and liver and wash in clean water. Further information on gathering Mahinga Kai can be obtained below.

“When a bloom of potentially toxic cyanobacteria is present in a lake, there is a possibility of cyanobacteria and toxins being transported downstream.

People are advised to avoid contact with the downstream water bodies,” says Dr Pink.

Environment Canterbury monitors the lake weekly while the warning is in place and the public will be advised of any changes in water quality that are of public health significance.

Facts about cyanobacteria:​