January 18, 2017
Health Warning - Algal bloom in Lake Forsyth/Te Roto o Wairewa
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 dogs, should avoid Lake Forsyth/Te Roto o Wairewa until the health warning has been
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, 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.”
The type of cyanobacteria currently present in high concentrations is Anabaena, which typically forms green globules
that float in the water column.
“Animals that show signs of illness after coming into contact with algal mats should be taken to a vet immediately,” Dr
Consumption of fish and shellfish should also be avoided because they can concentrate toxins, he says.
“If fish are eaten, remove the gut and liver and wash in clean water.”
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:
• 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.
Or contact Community and Public Health on (03) 364 1777.