A health warning has been issued for Lake Rotoehu after a bloom of potentially toxic blue-green algae was found.
"This health warning means that people should avoid any activity which results in contact with the lake water," Medical officer of health for Toi Te Ora Public Health Dr Jim Miller said.
He said swimming or water skiing could expose people to the toxins and contact with it could cause skin rashes, stomach upsets, and in some cases tingling around the mouth, headaches, breathing difficulties and visual problems.
Contact with water or inhalation of droplets affected by blooms of blue-green algae can also cause asthma and hayfever attacks in some individuals, he said.
"This current health warning reminds us of the importance of doing your own check on the water before you use it, watching out for algal blooms or other signs of possible changes in water quality before jumping in."
He advised people to "look before you leap" in Bay of Plenty water and if the water looked discoloured, smelled unusual, or if there was scum or black or brown algae on the surface
to swim or play somewhere else and don't eat shellfish from the area.
"After rainfall, water is likely to be contaminated with animal faeces from rural and urban run-off. As a precaution, avoid swimming in rivers, streams, lakes or estuaries for two to three days after heavy or prolonged rainfall, even for sites that usually have good water quality."
He said choosing a healthy spot to swim could help prevent tummy bugs, sore throats and skin infections this summer.