PORTAGE, Ind. (AP) — The Indiana Department of Environmental Management has cited U.S. Steel for causing a foamy discharge into a northwestern Indiana waterway that flows into Lake Michigan.

The department says the discharge into the Burns Waterway is a violation of U.S. Steel’s wastewater permit. The department gave the company 30 days to explain steps it took to correct the problem, which was observed last month.

U.S. Steel says tests didn’t detect a highly toxic form of chromium spilled from the plant in April 2017 and showed other pollutants were below permitted levels.

Surfrider Foundation and Chicago sued U.S. Steel over that spill . A Justice Department proposal would require U.S. Steel to pay civil penalties and damages . Surfrider on Thursday was given approval to intervene in that case.