The health warning issued in December 2017 for Lake Whangape has now been lifted, after two consecutive tests showed cyanobacterial levels to be once again below the warning level. Lakes Waahi, Waikare and Ngaroto continue to have cyanobacterial health warnings in place. Lake Hakanoa the other lake that is tested regularly, currently remains below the warning level for cyanobacteria.
Waikato DHB’s Medical Officer of Health Dr Richard Hoskins recommends that where cyanobacteria health warnings are in place, 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,” said Dr Hoskins
“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,” he 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.
Lakes Waikare, Ngaroto and Waahi have been found to have cyanobacteria biovolumes above the cut-off value for a health warning set at 1.8mm3/L. Biovolume is the measure used to decide when a health warning should be issued.
Testing is carried out by Waikato Regional Council monthly during the warmer months, and two monthly over the winter. The lakes which are tested may indicate, to some extent, cyanobacterial levels in other shallow lakes in the region.
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.
Waikato Regional Council no longer routinely tests Lake Kainui and Puketirini; however, caution is still advised for users of this lake because of its history of cyanobacterial blooms.
Waikato DHB’s 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 Population Health on (07) 838 2569.
Up-to-date information on cyanobacterial cell counts is available from local councils and Waikato Regional Council.