PORTAGE, Ind. (AP) — Indiana Dunes National Park closed all of its beaches and a northwest Indiana water utility shut down an intake facility after an orange substance apparently spilled from a U.S. Steel plant into a Lake Michigan tributary.

Portage Mayor Sue Lynch says she began receiving calls about 5:50 p.m. Sunday about the unknown substance appearing in the water near the outfall of the U.S. Steel Midwest plant in Portage and traveling toward Lake Michigan along the Burns Waterway.

That tributary is located about 30 miles east of Chicago. A message seeking comment from U.S. Steel was left Monday morning by The Associated Press.

The Times of Northwest Indiana reports the Indiana Department of Environmental Management was investigating.