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Published: 2003-06-16 00:00:00

Levels of blue green algae have begun receding in several Waikato waterways, but health warnings continue on some lakes.

This week’s Environment Waikato Environment Committee heard that Lakes Waahi, Whangape, Hakanoa, Kainui and Ngaroto still had warnings and staff continued to monitor selected waterways until the blooms subsided. The public were being kept informed with media releases and website updates as well as contact with affected groups.

Programme Manager Chris McLay said the algal problem peaked in the Waikato River in early January. The blue green algal bloom was present from Lake Ohakuri to Tuakau, but was no longer being recorded in the River. Lake Taupo also had a bloom in March which exceeded water quality guidelines in two bays, and in April a new type of algae was reported in Lake Karapiro, which had since disappeared.

The algae were naturally occurring, persistent in shallow lakes and responded to favourable climate, water with little flow and worsened by increased nutrient levels. They had been reported in the Waikato for at least 20 years, and the warm, sunny and calm summer weather was the reason for the increased incidencethis year.

They could not be easily controlled, and if similar conditions occurred the blooms would cause more problems in future, he said. They had affected drinking water suppliers, recreational users, duck hunters and food gatherers.

There were limited options for treating the blooms. Adding chemicals may not be acceptable in New Zealand, their success could not be guaranteed and their use could actually encourage resistance. He said Environment Waikato would work with Public Health and district councils on monitoring and response to the blooms should they reappear next summer.