A potentially toxic algal bloom has been found in Lake Taupo – and Environment Waikato says it highlights the need for changes to the way the lake’s catchment is managed.

Last week a number of bathers in the lake complained to Environment Waikato about “small particles, like confetti” in the water at various sites. The Council tested samples from six sites between Kinloch and Kuratau where the main complaints had come from.

Testing showed a wide area had been affected by the bloom, which contained a potentially toxic blue-green algae and a green algae, both of which had been found in the lake in previous summers. About 65 percent of the samples was made up of the potentially toxic variety.

Water scientist Bill Vant said cell counts were reported to the Medical Officer of Health for Pacific Health, Dr Phil Shoemack. Cell counts showed the density of the algae varied from about four cells per millilitre at Kinloch to about 1260 cells at Kawakawa Bay, while an estimate of cells from a sample from Te Hapua Bay showed counts as high as 6000 to 7500.

"Once levels exceed 2000 cells per ml the water is not safe for drinking and once over 15,000 cells per ml the public would be advised to avoid having any recreational contact with the water," Dr Shoemack said.

“Apart from the Te Hapua Bay sample, counts are relatively low. The high sample is from a relatively remote location, indicating a low health risk.”

Environment Waikato Resource Information Group Manager Dr Tony Petch said blooms were one of the reasons the Council was developing changes to control pollutants from surrounding land entering the lake. The controls were necessary to prevent further enrichment of the lake, which could result in more blooms.

“Normally we would not expect such a bloom in a lake like Taupo, because it is cleaner and colder than the places blooms are usually found. Human activity is known to make these blooms worse and that is one of the reason we are developing methods to protect the lake.”

Dr Shoemack said a number of community water supplies were taken directly from the lake but at this stage no health risks were apparent.

“Cyanobacteria are present in fresh water throughout the world, and blooms depend on various factors including climatic conditions, nutrient levels, and the amount of sunlight.”

Pacific Health, Taupo District Council and Environment Waikato will continue to keep an eye on the bloom and test the water.

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