Extensive rain prompted the St. Clair Region Conservation Authority to issue a water safety statement.
Over 24 hours the authority says the watershed absorbed up to 40 mm of precipitation and another 10 mm to 15 mm was possible Friday.
Director of Water Resources Girish Sankar says the public is urged to stay away from swollen waterways.
"The rain event has been happening over the last 24-36 hours, so the ground is really saturated, which is really key -- because where you expect the top of the bank of the river could be, may not be the case," says Sankar. "It could be much closer to where you're standing and because the levels are really high and it's slippery, there's a chance that somebody can slip into the water."
Sankar says water levels on the Sydenham River and its tributaries will be pushed to top of bank over the next few days.
Drains, floodplains and smaller watercourses in upstream areas will experience localized flooding in some areas.
Conditions are expected to moderate early next week once flows return to normal conditions.
Pretty Rd is closed between Stanley and McCallum Lines in St. Clair Township due to flooding.