Chicago waterways long used to carry away the city’s waste must be cleaned up expeditiously so residents can play in them, the U.S. Environmental Protection Agency told state officials on Thursday.

“A decade of investments in walkways, boat ramps and parks has provided people with access to the water — and now we need to make sure that the water is safe,” Susan Hedman, the agency’s Midwest regional administrator, said in a statement.

Boaters commonly ply the city’s rivers and canals, and residences have replaced some industries along the waterways in recent years. But users are warned against extensive contact with the water.

The agency informed the Illinois Pollution Control Board that if it does not promptly adopt higher standards for waters in the North and South Branches of the Chicago River, the North Shore Channel, the Cal-Sag Channel and the Little Calumet River, the agency will use its power under the U.S. Clean Water Act to do so.