Risks include skin and eye irritation, allergies like hayfever and asthma and stomach upsets
People are being warned to avoid contact with water in the Waikato shallow lakes because of cyanobacteria.
While it does not affect everyone, Waikato District Health Board says the risks include rash, skin andeye irritation, allergy symptoms such as hayfever and asthma and possibly stomach upsets such as diarrhoea and vomiting.
The lakes are in farmland north of Huntly.
A cyanobacterial health warning has been reinstated at Lake Whangape after the latest monitoring results from the six shallow lakes which are routinely tested. Warnings remain in effect at Kainui and Waikare.
Waikato medical officer of health Dr Dell Hood said, "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 summertime conditions generally increase the growth of algae. Users must consider the possibility of cyanobacterial blooms in any water body before they use it - at any time of year."
Dr Hood said test results should be used for general guidance only, as cyanobacteria and their toxins would not be evenly spread through any lake and might be concentrated in some areas by wind and water movements.
"During blooms, lakes should not be used for any activity which involves skin contact with the water.
"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.
The board's Population Health Service wants to hear about health problems which followed exposure to any of the Waikato lakes.
