U.S. Steel Corp. said the cause of discoloration Monday in the Burns Waterway was due to “elevated concentrations of iron” at an outfall its Midwest Plant in Portage.

The company said there are no indications of a release of hexavalent and total chromium beyond what it is permitted to release. U.S. Steel has been penalized in the past for multiple spills of those substances at toxic levels.

“Preliminary sampling results have shown that we remain in compliance with numeric permit limits. Analysis of the water from the outfall taken during the time of the incident showed elevated concentrations of iron causing the discoloration. There are no indications of permit level exceedances for hexavalent and total chromium, as those sampling results came in well below permit limits,” the company said in a written statement.

U.S. Steel said it shut down the Midwest Plant as a precaution and will continue to collect samples.

The Indiana Department of Environmental Management said it was investigating the discharge, but has not yet released its own assessment of the discharge. The agency said that investigators had not seen any dead fish or other wildlife, often an indicator of a chemical spill.

Portage Mayor Sue Lynch told multiple news outlets that residents began reporting the appearance of an unknown, rusty-colored substance in the water near an outfall at the plant in the Burns Waterway that then traveled towards Lake Michigan.

The National Park Service closed all of its beaches at the Indiana Dunes National Park and said they will remain closed.

Indiana American Water said it shut down its Ogden Dunes treatment facility temporarily as a precautionary measure, but the company said there has been no impact on the raw water it draws .

A federal court recently approved an agreement between U.S. Steel and the U.S. Department of Justice over a 2017 spill at the Midwest Plant that released hundreds of pounds of hexavalent chromium into the Burns Waterway.

The agreement requires the company to pay a $601,242 civil penalty and reimburse agencies for the costs they incurred while responding to the spill.

The consent decree also requires U.S. Steel to adhere to plans approved by the EPA and IDEM for facility wastewater operation and maintenance, preventive maintenance and chromium and wastewater process monitoring.

The facility has had multiple discharge events since 2017, including an additional chromium release in Oct. 2017, effluent limit violations in Nov. 2017 and multiple “scummy discharges” of what was later determined to be oil and grease and sulfuric acid.