CHICAGO (AP) — An Illinois environmental group is suing the owner of a shuttered power plant where contaminants from old coal ash ponds are seeping into a river used for recreation.

Prairie Rivers Network claims in the suit Wednesday that Dynegy Midwest Generation is violating the Clean Water Act by allowing heavy metals to seep from the riverbank along the Middle Fork of the Vermilion River.

A 17-mile portion of the river designated as a National Scenic River flows along the eastern boundary of the former Vermilion Power Station about 135 miles (217 kilometers) south of Chicago.

The plant, closed in 2011, left more than 3 million cubic yards (2.29 million cubic meters) of ash.

Dynegy didn’t immediately respond to a request for comment, but has said it’s working on a closure plan.