The Bay of Plenty Regional Council is treating an algal bloom in Lake Okaro near Rainbow Mountain.

The council is using a modified zeolite mineral to deal with the toxic blue-green bloom.

Blue-green algae laps alongside this lake.

The lake was treated at the weekend with the mineral to knock out the algae, which has taken the lake into a ‘red zone' in the council's ongoing monitoring programme.

Lake operations manager Andy Bruere says 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 alga, as it did when we had a bloom in Lake Rotoiti in February this year.”

Lake Rotoiti was treated earlier in the year to prevent the bloom of toxic blue-green algae.

The aim of the treatment was to avert the need for health warnings on the lake.

'We have experience with Aqual P on Lake Okaro and tests have shown it's safe to use in the natural environment.

'It was applied to the 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,” says Andy.

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

He says the product is not expected to cause any health effects for animals and monitoring after previous applications at Lake Okaro had identified no harmful effects.

Andy says the Aqual P slurry was applied from a helicopter and a comprehensive monitoring programme will continue for six weeks after the application.

He says it will take several days to determine if the dosing was successful.

A health warning was issued for Lake Okaro 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 Okaro 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, the regional council asks people to avoid entering the water and to keep pets away.