Toronto Public Health says splashing around at two of the city's beaches may not be the best idea right now.
They have warning signs up at Cherry Beach and Sunnyside Beach. Water tests there are showing higher than normal levels of E.Coli.
Mahesh Patel with Toronto Public Health tells Newstalk 1010, this week's big rainfall is to blame.
He says rain water can wash contaminants sitting on impervious surfaces into rivers and streams which run into Lake Ontario. And there could be more than E.Coli to worry about.
"If you find that, that means there are other pathogens or micro-organisms that can be harmful to health", explains Patel.
While Cherry and Sunnyside Beaches are open, it's bather beware.
"If possible, don't go and swim because there's an increased chance of getting an infection."
Patel says it is possible the water could be given a green light as early as Saturday. Public Health tests water at public beaches daily, including on weekends.