Canterbury DHB’s Community and Public Health unit has issued a health warning after potentially toxic blue-green algae (planktonic cyanobacteria) was found in Te Roto O Wairewa/ Lake Forsyth.

While a previous bloom of the cyanobacterium Anabaena has cleared (and the previous warning was lifted on the 15^th of February 2022), the species of cyanobacteria Nodularia spumigena is now present in high densities. Cell densities of this species have increased rapidly.

People should avoid the Lake and animals, particularly dogs, should not be allowed near the water until the health warning has been lifted. 

Dr Cheryl Brunton, 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 Brunton says.

No one should drink the water from the lake at any time. Boiling the water does not remove the toxin.

Animals that show signs of illness after coming into contact with algal mats or scums 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.

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:

• Cyanobacteria 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.

For further details visit: https://www.lawa.org.nz/explore-data/canterbury-region/

Or contact Community and Public Health on (03) 364 1777: https://www.cph.co.nz/your-health/recreational-water/

For more information about Mahinga Kai: https://www.cph.co.nz/wp-content/uploads/saf0112.pdf

ENDS