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Algae treatment for Lake Rotoiti

Monday, 21 February 2011 12:00 a.m.

Bay of Plenty Regional Council is treating Okawa Bay on Lake Rotoiti today with a product to prevent potentially toxic blue-green algae blooming on the lake.

Regional Council Lake Operations Manager Andy Bruere said the Regional Council had been alerted to a risk of the harmful algae forming in its routine monitoring, and from its environmental advisors, including Professor David Hamilton of Waikato University.

The aim of the treatment - with a modified zeolite product called Aqual P - was to avert the need for health warnings on the lake if a predicted bloom occurred. The presence of blue-green algae can close the lake to swimmers and boaties.

"The Regional Council has experience with the application of Aqual P on Lake Ōkaro, and tests have shown it is safe to use in the natural environment. It was applied to that lake in 2007 and 2009 to deal with eutrophication problems (where nutrients enter the lake and deplete oxygen). The product will rapidly settle and flocculate algae, and lock up phosphorus in the water column."

Mr Bruere said the product is not expected to cause any health effects for animals. Monitoring after applications at Lake Ōkaro had identified no harmful effects from the use of this product.

"This option is being trialled at Okawa Bay because the algae is potentially toxic, and the location is conducive to the technique," he said.

"We have needed to move quickly, due to the potential for algae numbers to increase rapidly under current weather conditions. We plan to apply a slurry to Okawa Bay which will lock up phosphorous and drop the algae to the bottom of the lake."

Regional Council staff met with Okawa Bay residents yesterday to explain the process, and are working with trustees of Maorī trust land being used as a base for the operation.

The slurry will be applied from a helicopter and should be completed within two hours. A comprehensive monitoring programme has been designed to determine the success of the application and ensure any effects are identified.

Algal bloom lowres (1)