Treatment for Lake Ōkaro’s algal bloom

20 December 2011

Bay of Plenty Regional Council has dosed Lake Ōkaro near Rainbow Mountain with a modified zeolite mineral to deal with toxic blue-green algal bloom visible in the lake.

The lake was dosed over the weekend with the mineral to knock out the algae, which has taken the lake into a ‘red zone’ in the Council’s on-going monitoring programme. Lake Operations Manager Andy Bruere said the substance, called Aqual P, is a naturally occurring mineral which has been changed in an industrial process to enhance its ability to take up phosphorus from the water.

“We believe this will knock out the algae, as it did when we had a bloom in Lake Rotoiti in February this year.”

Lake Rotoiti was dosed earlier in the year to prevent a bloom of harmful and toxic blue-green algae. The aim of the treatment was to avert the need for health warnings on the lake. The presence of blue-green algae can close the lake to swimmers and boaties.

“We have experience with 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,” he said.

“This application is for a very low dose application to specifically target the nuisance algae present.”

Mr Bruere said the product is not expected to cause any health effects for animals, and monitoring after previous applications at Lake Ōkaro had identified no harmful effects. The University of Waikato’s Chair in Lake Science Professor David Hamilton had designed a comprehensive monitoring programme to identify the success of the application and confirm environmental safety aspects.

Regional Council staff met with residents in the area to explain how the mineral works during the consent process. The Aqual P slurry was applied from a helicopter and a comprehensive monitoring programme will continue for six weeks after the application. It will take several days to determine if the dosing was successful, Mr Bruere said.

A health warning was issued for Lake Ōkaro last week. Contact with algal blooms can trigger asthma and hayfever, as well as causing skin rashes, stomach upsets and in some cases neurological effects such as tingling around the mouth, headaches, breathing difficulties and visual problems.

Signage has been erected at Lake Ōkaro advising of the algal bloom, and weekly monitoring of lakes and rivers will continue throughout the summer.

If water has a musty smell, appears murky with a blue or greenish tinge, or if there is a scum on the surface, people should avoid entering the water and keep pets away.

ENDS

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