As anticipated, testing late last month has confirmed that cyanobacterial cell counts have risen in Lakes Hakanoa and Whangape.  

As of this month, all the lakes which are regularly tested for cyanobacteria have health warnings in place due the presence of high cyanobacterial numbers.  

The tested lakes are Waahi, Waikare, Kainui, Ngaroto, Hakanoa and Whangape. Cell counts will most likely be rising in all shallow lakes as
summer progresses.    

"Waikato shallow lake users should always avoid contact with water which looks cloudy green or brown, or has scum forming even when there is no warning in place," said Waikato District Health Board medical officer of health Dell Hood.  

"Most lakes are not tested, and cell counts are likely to be rising in all of them as summer arrives."

In accordance with new national interim guidelines, warnings will soon be issued on the basis of 'bio volume' rather than cell counts.  

Bio volume is a measurement which takes into account not only the number of cells present but also their size.  

"Big cells can hold more toxins than tiny ones, so the size as well as the number is important in deciding when there might be a risk to human health," said Dr Hood.

"The change will be made as soon as sizes for all the different species of cyanobacteria found in our lakes and river have been calculated."

Dr Hood reminds the public that 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.

"During blooms, lakes should not be used for any activity which involves skin contact with the water," she said.

"If people choose to do this, they should shower and change their clothing as soon as possible afterwards, even if no symptoms are noticeable."

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

While not everyone will be affected, for some, the risks include rash, skin and eye irritation, allergy symptoms such as hay fever 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.

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

This allows recording of location, time, the activity taking place and length of time the problem lasted.  Follow-up testing may be done, depending on the situation.

Up-to-date information on cyanobacterial cell counts is available from local councils and Environment Waikato.

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