A cyanobacterial bloom or sudden massive episode of growth has occurred in Lake Whangape, which now joins Waikare in having a cyanobacterial health warning in place.  This is an anticipated seasonal event following on from longer hours of daylight and warmer weather.

The five other lakes which are routinely tested remain at acceptable levels of cyanobacteria, and do not have health warnings.  This includes Hamilton City’s Rotoroa (Hamilton Lake.)  However, it is likely that more health warnings will be required as summer progresses.

Waikato Regional Council is no longer routinely testing Lake Kainui but caution is always advised for users of this lake, because of its history of cyanobacterial blooms.  

As always, these test results should be used for general guidance only, as cyanobacteria and their toxins will not be evenly spread through any lake and may be concentrated in some areas by wind and water movements.  Cyanobacterial blooms can happen very quickly when conditions for growth are favourable. 

Waikato DHB medical officer of health Dell Hood said during blooms, lakes should not be used for any activity which involves skin contact with the water.

“Scums are a particular risk and contact with scums should be avoided.  If contact does occur, skin should be rinsed clean and clothing changed as soon as possible.  Because of their small size, this warning is particularly important for children,” said Dr Hood.

Swallowing water from lakes affected by blooms should also be avoided.

“If people still choose to use the lakes when warnings are in place, or 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.”

While not everyone will be affected, for some, the risks include rash, skin and eye irritation, allergy symptoms such as hayfever and asthma and possibly stomach upsets such as diarrhoea and vomiting. 

These effects may not appear until some time after contact with the affected water.  Long term exposure to cyanobacterial toxins may bring additional health risks.  Scums on any lake are likely to contain high levels of toxin.

Waikato DHB’s Population Health would like to be informed about health problems which develop after exposure to any of the Waikato lakes. 

“Up-to-date information on cyanobacterial cell counts is available from local councils and Waikato Regional Council website.

Health advice is available from Population Health (07) 839 8899 in and out of hours.

-Waikato District Health Board