Sampling carried out by the Otago Regional Council has shown the re-appearance of high concentrations of potentially toxic cyanobacteria (blue-green algae) at Lake Waihola and a new health warning has been issued for the lake following the removal of an earlier warning two months ago.

Visitors are advised not to use the lake for recreational purposes and observe warning signs until the warning has been lifted, while dog owners are also being warned to avoid allowing their pets swim in the lake until then as well.

Cyanobacteria can produce toxins that are harmful to humans and animals if swallowed or through contact with skin (such as may occur when swimming, water skiing or kayaking). Exposure to cyanobacteria may cause symptoms such as skin rashes, nausea, tummy upset, and tingling and numbness around the mouth or tips of fingers.

Anyone experiencing health symptoms after contact with contaminated water should visit their doctor.

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.

Cyanobacteria occur naturally but can increase rapidly during summer months. If the water is cloudy, discoloured, or has small globules suspended in it, all contact should be avoided. Not all cyanobacterial blooms are visible to the naked eye and toxins can persist after the bloom has disappeared.

Cyanobacterial concentrations can change quickly with changing environmental conditions (eg wind).

ORC monitors cyanobacteria weekly at Lake Waihola during summer, and the public will be advised of any changes in water quality that are of public health significance. Signage alerting the public to the presence of cyanobacteria will remain in place until two consecutive clear samples indicate it is safe .