October 25, 2013

Potentially toxic blue-green algae found in Lake Waihola

A potentially toxic algal bloom has appeared in Lake Waihola and the Tomahawk Lagoon.

ORC director of environmental information and science John Threlfall said a sample taken from the lake had confirmed that the toxic blue-green algae, which occurs naturally in a variety of water quality conditions, was present there.

At the moment the water in Lake Waihola looks very green. This is due to this algae species which belongs to’ or ‘cyanobacteria’ group of algae. This group of algae has the potential to produce a series of toxins which are then passed to the water; this can cause illness in people and animals.

Dr Threlfall said the degree of toxicity was impossible to accurately predict, however the algal samples would be tested for toxicity early next week. The results of this testing would provide more certainty about how toxic the bloom was.

Southern District Health Board Medical Officer of Health Dr Marion Poore said people swimming in water with increased levels of algal bloom have been known to develop allergic reactions: asthma, eye irritations, rashes, blistering around the mouth and nose, and gastro-intestinal disorders, including abdominal pain, cramps, and diarrhoea.

Any reaction depends on the type of toxins present, and the concentration of the toxin in the water. The higher the concentration of toxins and the longer the contact with the water, the more severe the symptoms are likely to be.

People should not swim in areas affected by the algae, and other water users, including fishermen and boat users, should exercise caution, Dr Poore said.

People could safely walk their dogs on the lakefront, provided they kept them well away from the water.

“In the case of illness or suspected illness after swallowing water containing algal bloom, seek advice from your doctor. If your animals become sick, contact your veterinarian immediately," Dr Poore said.

Dr Threlfall said: “We appreciate that a holiday weekend is upon us, and that swimming in the lake is a popular pastime, but we consider the safety and health of people and their animals to be paramount.”

The council has put up warning signs at the locations where the algae has been found, and will continue to monitor the situation, along with Public Health South.

Information leaflets are being distributed to various locations in the township, including local stores and tourism businesses. They are also available from the council’s head office at 70 Stafford Street, on the council’s website www.orc.govt.nz, or by phoning 0800 474082.

Dr Threlfall said people should be wary of the possible presence of toxic algae in rivers and lakes throughout the region this summer. ORC and PHS will continue to monitor the situation.

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