PORTAGE, Ind. (AP) — Preliminary tests indicate iron-contaminated wastewater that leaked from a northwestern Indiana steel plant into a Lake Michigan tributary presents no risk to public health, the Environmental Protection Agency said Wednesday.

U.S. Steel Midwest idled the plant in Portage, about 30 miles (48 kilometers) east of Chicago, as a precaution after it said a wastewater treatment facility experienced “an upset condition” that sent the rusty colored plume containing elevated levels of iron into the Burns Waterway on Sunday.

The EPA said it tested surface water samples taken near the plant's outfall.

Federal and state agencies were continuing to investigate the cause of the discharge, possible Clean Water Act compliance issues and impacts to the environment, the agency said.

The plant was back up and running Wednesday, according to The (Northwest Indiana) Times.

Indiana Dunes National Park also closed all of its beaches and the Portage Lakefront and Riverwalk until further notice and Indiana American Water shut down its Ogden Dunes treatment facility, both as a precaution.

On Wednesday, the National Park Service announced that the waters of all beaches at Indiana Dunes National Park were reopened.

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This story was first published on Sept. 29. It was updated on Sept. 30 to correct a reference to elevated levels of lead having leaked into the waterway. It was high levels of iron.