Algal bloom in Lake Forsyth

Tuesday February 20, 2018

The Community and Public Health division of Canterbury District Health Board has issued a health warning after potentially toxic blue-green algae (planktonic cyanobacteria) was found in Lake Forsyth/ Te Roto o Wairewa.

People and animals - particularly children and dogs - should avoid Lake Forsyth/Te Roto o Wairewa until the health warning has been lifted.

The type of cyanobacteria that is currently present in high concentrations is Nodularia spumigena which is a filamentous algae that can produce the hepatotoxin 'nodularin’. Filaments can (but do not always) aggregate in surface scums. No visible surface scums were sighted at the time of sampling.

Canterbury Medical Officer of Health Dr Ramon Pink 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, and 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." Dr Pink says boiling the water does not remove the toxin.

Animals that show signs of illness after coming into contact with algal mats 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.

Get more infromation on safely gathering mahinga kai.

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.

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.

Visit the Environment Canterbury website for more on swimming quality in Canterbury.

You can also contact Community and Public Health for more information on this health warning (03) 364 1777.

Facts about cyanobacteria:

  • The algae occur naturally but can increase rapidly during warmer months.
  • Avoid all contact if the water is cloudy, discoloured, or has small globules suspended in it.
  • Not all cyanobacteria blooms are visible to the naked eye and toxins can persist after the blooms disappear.
  • Cyanobacteria concentrations can change quickly with changing environmental conditions such as wind. Avoid contact with the water if a health warning is in place.
Page last reviewed: 20 February 2018
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