Lake Rotoroa in Hamilton is still considered a significant health-risk after tests in late May confirmed a bloom of blue-green algae in the water.
The Waikato Regional Council issued the lake with a health warning in mid-February after tests showing high numbers of cyanobacterial toxins there and in Lake Ngaroto near Te Awamutu.
Risk to the public, especially young children, remains high due to wind creating scums on the northern shore, particularly around the café and playground.
Children’s smaller size makes them particularly vulnerable, and dogs may also be at risk of illness.
The Hamilton City Council has warned people to ensure they and their pets avoid contact or drinking the water.
While not everyone will be affected, the risks include rash, skin and eye irritation, allergy symptoms such as hay fever and asthma and possibly stomach upsets such as diarrhoea and vomiting.
“During blooms, lakes should not be used for any activity which involves skin contact with the water,” said Waikato District Health Board medical officer Dr Dell Hood.
“If people still choose to do this when warnings are in place, they should shower and change their clothing as soon as possible afterwards, even if no symptoms are noticeable.”
Long term exposure to cyanobacterial toxins may bring additional health risks.
Dr Hood reminded lake users that test results should be used for general guidance only, as toxins would not be evenly spread.
The Waikato DHB Population Health Service would like to be informed about health problems which develop after exposure to any of the Waikato lakes.
Health advice is available from the Population Health Service (07) 839 8899 in and out of hours.