Up to 39,000 gallons of toxic chemicals leaked Sunday into the St. Clair River across the border near Sarnia, Ontario, forcing the closings of water plants serving tens of thousands of people.
The leak was reported Sunday morning at an Imperial Oil plant south of Sarnia. It was later contained.
Water from the St. Clair River flows into Lake St. Clair and then into the Detroit River and into Lake Erie.
Intakes were closed for water plants serving about 36,000 customers in several St. Clair County communities, said Jeffrey Friedland, the county's emergency management director.
The Detroit Water & Sewerage Department, which serves about 4 million customers, did not expect to be affected.