More than a million gallons of sludge spilled into the Kankakee River on Monday.
An explosion at a water treatment plant scattered debris and destroyed a Kankakee water department building.
No one was hurt.
But the blast caused sludge and raw sewage to leak into the river. The EPA says it did not get into Kankakee's drinking water.
The agency says it has not found any dead fish in the river, which could signal waste water was contained immediately.