Lake Forsyth algal blooms prompts health warning

People and animals are being warned to avoid Lake Forsyth/Te Roto o Wairewa after the discovery of a potentially toxic blue-green algae.

Dr Alistair Humphrey, Canterbury Medical Officer of Health says the algal bloom - planktonic cyanobacteria - can produce toxins harmful to humans and animals, and 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.

“No one should drink the water from the lake at any time. Boiling the water does not remove the toxin,” Dr Humphrey says.

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 going to be eaten, remove the gut and liver and wash in clean water before consuming.

Environment Canterbury monitors the lake and advises the public of any changes in water quality that are of public health significance.

This is the earliest seasonal algal bloom warning issued for Lake Forsyth in more than 10 years.

Facts about cyanobacteria:

• The algae occur naturally but can increase rapidly during warmer months.
• Algal blooms are caused by a combination of nutrients in the water (such as nitrogen and phosphorus), and favourable weather conditions (e.g. increased temperature, calm days).
• 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.