Cyanobacterialwarning Update - North Waikato Lakes, Ngaroto and Rotoroa (Hamilton Lake)

New health warnings are now in place for two more of the regularly tested lakes outside Hamilton. The lakes affected are Hakanoa, and Waikare, and now Waahi and Whangape as well, said Waikato District Health Board (DHB) medical officer of health Dell Hood.

Ngaroto remains below the warning level at the time of the most recent sampling, carried out in late October.

By contrast, Rotoroa in Hamilton City has for the time being had its health warning lifted, although with the warmer weather and longer days, it is likely that the recent persistent bloom will recur.

Waikato Regional Council 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 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. 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. Because of their small size, this warning is particularly important for children.

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

“If people still choose to use the lakes when warnings are in place, they should shower and change their clothing as soon as possible afterwards, even if no symptoms are noticeable.”

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 Waikato Regional Council. The Waikato Regional Council website: http://www.waikatoregion.govt.nz/Environment/Natural-resources/Water/Rivers/Waikato-River/Algal-Blooms-in-the-Waikato-region/

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

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