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Cyanobacterial warning update - North Waikato Lakes, Ngaroto and Rotoroa (Hamilton Lake)Monitoring results from late March have shown that cyanobacterial cells are at high levels in all five lakes which are routinely tested. The current bloom in Rotoroa (Hamilton Lake) has also become a more significant health risk, especially for small children.
Rotoroa has had a health warning since mid February due to the presence of high numbers of cyanobacterial cells. The risk to the public has this week increased considerably because the wind has caused cells to become concentrated and form scums, particularly around the northern shores of the lake. High levels of cyanobacterial toxin is present in this scum.
All contact with scums around the lake shore is hazardous to human health. Children’s smaller size makes them particularly vulnerable, and dogs may also be harmed.
There are now health warnings in place for all the lakes outside Hamilton which are regularly tested. Waahi has a new warning, and existing warnings remain in place for Ngaroto, Whangape, Hakanoa and Waikare.
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.
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 as in Rotoroa 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. 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.
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. Scums on any lake are likely to contain high levels of toxin.
The Waikato DHB Population Health Service 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 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.
Hamilton Lake specific advice is available from the Parks and Gardens Unit, Hamilton City Council (07) 838 6649.
Date: 31 March 2011
Mary Anne Gill
Waikato District Health Board
021 705 213