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Waikato Shallow Lakes Cyanobacterial Warning Update

Fuseworks Media
Fuseworks Media
Waikato Shallow Lakes Cyanobacterial Warning Update

Monitoring results from late August 2010 have shown that the human health threat from cyanobacteria in all the tested lakes is now acceptably low, apart from Lake Waikare, where a health warning remains in place as levels are persistently high..

It is likely that warnings will need to be reinstated within a few months as the longer hours of sunshine and warmer temperatures provide better conditions for the algae to grow.

Lake Ngaroto in particular at 1.7 is not far below the warning level of 1.8 cubic mm/L, but any of the tested lakes may need to have a warning reinstated after the next tests are taken in October.

These warnings are based on the now accepted biovolume measurement, where the cut off point is 1.8 mm3/L. This reflects the importance of the size of the cells as a more useful indicator of how much toxin may be in the water.

Environment Waikato is no longer routinely testing Lake Kainui.

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.[1]

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 Service are moving to full use of the new guidelines as information about the cell size of various species found in local lakes is measured.

At this point, warnings will be 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.

As in previous years testing will take place less frequently over the colder months. The next samples will be collected in late October

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

"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 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.

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.

The Environment Waikato website has up to date results.

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

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