Wellington, Dec 10 NZPA - Four shallow Waikato lakes have health warnings in place due to high algae (cyanobacterial) cell counts found after testing by Environment Waikato. Lake Waahi, west of Huntly, Lake Waikare, north of Huntly, Lake Kainui, north of Hamilton, and Lake Ngaroto, northwest of Te Awamutu, have all been affected.

"Cell counts will most likely be rising in all shallow lakes as summer progresses," said Waikato District Health Board medical officer of health Dell Hood. "Waikato shallow lake users should always avoid contact with water which looks cloudy green or brown, or has scum forming even when there is no warning in place. "Most lakes are not tested, and cell counts are likely to be rising in all of them as summer arrives."

The test results should be used for general guidance only, as cyanobacteria and their toxins would not be evenly spread through any lake and may be concentrated in some areas by wind and water movements, Dr Hood said. "During blooms, lakes should not be used for any activity which involves skin contact with the water," she said.

"If people choose to do this, they should shower and change their clothing as soon as possible afterwards, even if no symptoms are noticeable." Swallowing water from lakes affected by blooms should also be avoided. While not everyone would be affected, for some, the risks include rash, skin and eye irritation, allergy symptoms such as hayfever and asthma and possibly stomach upsets such as diarrhoea and vomiting, she said.

The effects might not appear until some time after contact with the affected water, she said.