Public health officials issue warning after toxic algae found in Lake Hood, Ashburton

Te Mana Ora is warning people to avoid Lake Hood, south of Ashburton after toxic blue-green algae that can cause skin rashes and nausea was found.

The agency said people should not go near the lake and animals, particularly dogs, should not be allowed near the water until the health warning has been lifted.

A spokesperson said the type of planktonic cyanobacteria present is Dolichospermum (formerly called Anabaena) which can be green globules floating in the water column or form surface scums or sheens.

National Public Health Service Medical Officer of Health Dr Cheryl Brunton said the algal bloom can produce toxins harmful to humans and animals.

“People should avoid contact with the water until further notice,” she said.

“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.”

The agency also stressed no one should drink the water from the lake at any time and boiling the water does not remove the toxin.

Animals that show signs of illness after coming into contact with algal mats or 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 the remainder in clean water.

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

“People are advised to avoid contact with the downstream water bodies.

“Environment Canterbury monitors the lake weekly during summer and the public will be advised of any changes in water quality that are of public health significance.”

Facts about cyanobacteria

· Cyanobacteria occur naturally but can increase rapidly during warmer months.

· Algal blooms are caused by a combination of nutrients in the water (such as nitrogen and phosphorus), and favourable weather conditions (e.g., increased temperature, calm days).

· If the water is cloudy, discoloured, or has small globules suspended in it, avoid all contact.

· Not all cyanobacterial blooms are visible to the naked eye and toxins can persist after the blooms disappear.

· Cyanobacterial concentrations can change quickly with changing environmental conditions (e.g., wind). If a health warning is in place avoid contact with the water.