A potentially toxic blue-green algae's bloomed on Lake Ohakuri, north of Taupo

Routine testing by Waikato Regional Council showed the overgrowth.

Bay of Plenty and Lakes Districts medical Officer of Health Dr Neil de Wet is warning people to avoid the lake water.

He says people could be exposed to toxins just by inhaling droplets of water spray.

Contact with the water could cause asthma, hayfever, skin rashes - and even neurological effects like tingling around the mouth and visual problems.