The Hawke's Bay Regional Council has confirmed significant contamination of the Clive and Karamu rivers from a sewage spill earlier this week.
Vandals reportedly damaged a sewer pipe in Havelock North on Wednesday night, and an unknown quantity of sewage spilt into the stream.
People are being advised not to swim or gather food from the waterways until further notice, because of the risk of infections affecting the stomach, skin, eyes and ears.
The council says water samples indicate a significant level of faecal contamination in the rivers. It says all irrigators who take water for crops have been contacted.
The region's Medical Officer of Health, Dr Nick Jones, says that until sampling shows less contamination, people should avoid any activity in the water.
