A health warning has been issued for Lake Ohakuri and Lake Maraetai after tests confirmed a bloom of potentially toxic blue-green algae.

The blooms were confirmed through routine monitoring results provided by Waikato Regional Council.

Lake Ohakuri is south west of Ngakuru, while Lake Maraetai is in Mangakino.

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Medical Officer of Health Dr Jim Miller said the health warning meant people should avoid any activity which resulted in significant contact with the lake water.

Contact with water affected by blooms of blue-green algae can cause asthma and hayfever attacks in some. Contact with the blue-green algae can also cause skin rashes, stomach upsets, and in some cases neurological effects such as tingling around the mouth, headaches, breathing difficulties and visual problems.

Signage will be erected at both lakes advising potential lake users about the algal bloom.

Dr Miller said the public should always be cautious for signs of algal blooms if using lakes.

"Algal blooms can develop rapidly and unpredictably and can sometimes produce toxins that are harmful for people as well as animals. If the water looks discoloured, has an unusual smell, or has green or brown particles suspended in it then it is best to avoid contact with it."

Up-to-date information on health warnings for the Bay of Plenty and Lakes districts is available through these channels:
- Phone: 0800 221 555
- Website: www.ttophs.govt.nz/health_warnings
- Fact Sheet: www.ttophs.govt.nz/vdb/document/43
- Facebook: www.facebook.com/toiteora
-Twitter: www.twitter.com/toiteora
- Email alerts for subscribers: www.ttophs.govt.nz/alert