Samples have been taken from the lake and results are pending.
"This health warning means that people should avoid any activity which results in contact with the lake water," medical officer of health Dr Jim Miller said.
Contact with water affected by blooms of blue-green algae can cause asthma and hay fever attacks in some individuals. 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 has been erected at Lake Ohakuri advising potential lake users about the algal bloom.
As summer nears, Miller advised the public to keep an eye out for signs of algal blooms if using lakes in the region and would like to thank the members of the public for informing authorities.
"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 floating in it then it is best to avoid contact with it."
The warning will be reviewed when more information comes to hand.
