A new health warning has been issued on 1 December for Lakes Whangape and Ngaroto. Lake Whangape has had a rise in the cyanobacteria biovolume to 5.8 mm3/L and Lake Ngaroto to 3.0 mm3/L . Biovolume is the measure used to decide when a health warning should be issued, with the cut-off value for a health warning set at 1.8mm3/L.
Lake Waikare continues to have a cyanobacterial health warning in place with the latest level increasing to 31.4 mm3/L. Lakes Hakanoa, Waahi and Rotoroa (Hamilton Lake) the other lakes that are tested regularly, all currently remain below the warning level for cyanobacteria.
Testing is carried out by Waikato Regional Council monthly during the warmer months, and two monthly over the winter. Hamilton City Council is responsible for testing Lake Rotoroa (Hamilton Lake). 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.
“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 Anita Bell 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,” 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.
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.