Health Warning – Algal Bloom in Lake Forsyth (Te Wairewa)

Thursday November 3, 2011

​The Community and Public Health division of Canterbury District Health Board have issued a health warning this week after toxic blue-green algae (planktonic cyanobacteria) were found in Lake Forsyth/ Te Wairewa.

People should stay out of the water at this site until the health warnings have been lifted. Toxic algae are particularly dangerous for dogs, so they should be kept away from the water. 

Canterbury Medical Officer of Health Dr Alistair Humphrey says the algal bloom can produce toxins harmful to humans 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 after contact with contaminated water, visit your doctor immediately,” Dr Humphrey says.

“No one should drink the water from the lake at any time, even if it has been boiled because boiling does not remove the toxin. 

Animals should be taken to a vet immediately if they come into contact with water contaminated by the algal bloom or if they display any unusual symptoms.

Fish and shellfish can concentrate toxins and their consumption should be avoided.

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

Facts about cyanobacteria:

  • The algae occur naturally but can increase rapidly during warmer months.

  • 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.

For further information visit Environment Canterbury.

Or contact Community and Public Health on (03) 364 1777.​

Page last reviewed: 12 February 2014