Lake Ngaroto has been issued with a health warning due to a cyanobacterial bloom. This is an anticipated seasonal event following longer daylight hours and warm weather.
Lakes Whangape and Waikare already have cyanobacterial health warnings in place and Waahi, Hakanoa and Rotoroa (Hamilton Lake), the other lakes that are tested regularly, all currently remain below the warning level for cyanobacteria.
Cyanobacteria are a form of algae which can produce toxins harmful to the health of humans and animals exposed to or swallowing the water where the algae are growing.
Testing is carried out by Waikato Regional Council monthly during the warmer months. The lakes which are tested may indicate, to some extent, cyanobacterial levels in other shallow lakes in the region.
"During blooms, lakes should not be used for any activity that involves skin contact with the affected water. Swallowing water from lakes affected by blooms should also be avoided," medical officer of health Dr Dell Hood said.
"Scums are a particular risk because they contain a high level of toxins. If contact with scum does occur, skin should be rinsed clean and clothing changed as soon as possible. This warning is particularly important for children.
"If people still choose to use the lakes when warnings are in place, or any other lake where there are visible changes to water colour, they should shower and change their clothing as soon as possible afterwards, even if no symptoms are noticeable," she said.
Symptoms include rash, skin and eye irritation; allergy symptoms such as hayfever and asthma; and possibly stomach upsets including diarrhoea and vomiting.
These symptoms may not appear until some time after contact with the affected water. Long-term exposure to cyanobacterial toxins may cause additional health risks.
Waikato Regional Council no longer routinely tests Lake Kainui; however, caution is still advised for users of this lake because of its history of cyanobacterial blooms. Cyanobacterial blooms can happen very quickly when conditions for growth are favourable.
Test results should be used for general guidance only, as cyanobacteria and their toxins are not evenly spread through any lake and may be concentrated in some areas by wind and water movements.
Waikato DHB Population Health Service would like to be informed about health problems that develop after exposure to any of the Waikato lakes. Health advice is also available from the Population Health Service on (07) 839 8899 in and out of hours.
Up-to-date information on cyanobacterial cell counts is available from Waikato Regional Council and other local councils.