23 December 2014
Health Warning for Lake Ngaroto: Cyanobacterial Update
A new health warning has been issued today for Lake Ngaroto near Te Awamutu; due to a cyanobacterial bloom.
This is an anticipated seasonal event following longer hours of daylight and warmer weather. The lake has had a rise in
the cyanobacteria biovolume to 4.5mm3/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.
Lakes Waikare, Hakanoa and Lake Rotoroa (Hamilton Lake) continue to have cyanobacterial health warnings in force.
Lakes Waahi, and Ngaroto, 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.
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 Felicity Dumble 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.
Waikato DHB’s Population Health 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 on (07) 838 2569.
Up-to-date information on cyanobacterial cell counts is available from local councils and Waikato Regional Council.
ENDS