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
lifted.
Recent testing indicated high numbers of the potentially toxic cyanobacterium Aphanizomenon were present in the water of Lake Forsyth/ Te Roto o Wairewa. The cyanobacteria is not always visible, however this
filamentous algae can form dense blooms near the surface.
Dr Alistair Humphrey, 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 Humphrey says.
No one should drink the water from the lake at any time, Dr Humphrey 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.
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.
For further information visit https://www.ecan.govt.nz/your-region/your-environment/water/swimming-water-quality/
Or contact Community and Public Health on (03) 364 1777.
ENDS