Waikato Shallow Lakes Cyanobacterial Warning Update


Two lakes have health warnings lifted

The threat to human health from cyanobacteria in Lakes Hakanoa and Waahi is now acceptably low, according to recent monitored results.

However, cyanobacteria counts in Lakes Whangape and Waikare remain above the warning level meaning they are likely to cause health problems in people who come into contact with the water. Ngaroto was not tested in May.

Environment Waikato is also no longer routinely testing Lake Kainui.

New guidelines for measuring 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 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 1.8mm3/L.

As in previous years testing will take place less frequently over the colder months. The next samples will be collected in late June, after which the interval between tests will be two months.

Waikato DHB medical officer of health Dell 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,” 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.

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.

The Environment Waikato website has up-to-date results:
http://www.ew.govt.nz/Environmental-information/Rivers-lakes-and-wetlands/healthyrivers/Waikato-River/Algal-Blooms-in-the-Waikato-region/#Heading4

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

ENDS

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