Parents at Ashley School in Canterbury want to know if their children are safe after they swam in the contaminated Ashley River last week.
University of Otago professor of public health Michael Baker says people should avoid swimming in rivers unless they know the water is clean enough. Photo: RNZ/Philippa Tolley
Fish and Game revealed this week three Canterbury rivers, including the Ashley River, had traces of an antibiotic-resistant E coli.
There is also a pathogen that can cause kidney failure.
University of Otago professor of public health Michael Baker said people should seek medical help if they had vomiting, stomach cramps or diarrhea.
"The incubation period for this infection is typically three to four days, but it does have quite a range, sometimes one to ten days," Professor Baker said.
"Generally if you've got by for a week without any symptoms, you're unlikely to develop illness."
Unless people know about the water quality in an area, they should not swim or should avoid putting their heads under the water, he said.