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 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.
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, 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 Ramon Pink says.
“No one should drink the water from the lake at any time.” 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.
Further information on gathering Mahinga Kai can be obtained below.
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 until the warning is lifted 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/