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Waikato shallow lakes cyanobacterial warning updateFour lakes now have health warnings in place
Monitoring results from late November 2010 have shown that cyanobacterial cells are multiplying in four of the five lakes which are routinely tested.
This is an expected consequence of the warm weather we are currently experiencing.
There are health warnings in place for Lakes Ngaroto, Whangape, Hakanoa and Waikare.
Ngaroto and Whangape are the two lakes with the new warning this month.
Environment Waikato is no longer routinely testing Lake Kainui but caution is always advised for users of this lake, because of its history of cyanobacterial blooms.
A recent single test carried out on the water of Kainui confirms that the cyanobacterial levels are well above the human health warning level of 1.8 mm3/L.
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.
Even just a few days of warm calm sunny weather could produce rapid algal growth, which would be noticeable to users by discoloration of the water or unusual scums forming near the margins.
New guidelines for measuring and responding to cyanobacteria in fresh water recreation sites were published last summer. 
Warning levels now take into account not only the number of known toxin producing cells present but also their size.
In recent years some warnings may have been overly cautious when the cyanobacterial species present in large numbers was known to have a small cell size.
Environment Waikato and Waikato District Health Board’s Population Health have moved to full use of the new guidelines as information about the cell size of various species found in local lakes is measured.
Warnings are now issued when the ‘biovolume’ exceeds 1.8 mm3/L. Warnings are based on the likelihood of cyanobacterial toxin being in the water, not on actual toxin measurements.
“During blooms, lakes should not be used for any activity which involves skin contact with the water,” said Population Health medical officer of health Dell Hood.
“If people still choose to do this when warnings are in place, 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 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.
Population Health 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.
Date: 14 December 2010
 Ministry for the Environment and Ministry of Health. 2009. New Zealand Guidelines for Cyanobacteria in Recreational Fresh Waters - Interim Guidelines.