Authorities closed several beaches on Lake Michigan on Friday after a US steel plant leaked oil into a tributary for the second time in less than two weeks, the Associated Press reported.

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The glow was seen on Burns Waterway outside the US Steel Midwest plant in Portage, Indiana, Thursday morning, company spokeswoman Amanda Malkowski told the AP. However, it was no longer visible till 8 pm

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Malkowski said the current boom has absorbed the glow in a 120-square-foot area The Northwest (Indiana) Times.

“No flashes were observed in Lake Michigan or entering the lake,” Malkowski said. “We continue to investigate the cause.”

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For more reporting from the Associated Press, see below.

US Steel temporarily disabled the plant about 30 miles (48 kilometers) east of Chicago as a precaution, but operations were back to normal by Thursday night, she said.

The Indiana Department of Environmental Management was investigating, spokesman Barry Snead said.

The US Environmental Protection Agency did not immediately comment on Thursday’s holiday.

As a precaution, Indiana Dunes National Park closed access to the lake from the neighboring Portage Lakefront and Riverwalk on Thursday, spokesman Bruce Rowe said. He added that visitors can still walk along the lake, but not in the water, and that “all other national park beaches are open at this time.”

A city official said the community near Ogden Dunes has also closed its beachfront access to Lake Michigan.

Indiana American Water’s Ogden Dunes water treatment facility remained online and the spill was not expected to affect the source water of Lake Michigan, spokesman Joe Lofmiller said.

“We are closely monitoring our source water monitors and are in contact with all parties involved regarding this situation,” he said on Thursday.

That treatment plant was deactivated by the water utility for about a week starting in late September after US Steel’s portage plant released iron-stained wastewater into the Burns Waterway.

That rust-colored discharge caused the Portage Riverwalk and lakefront and beaches in Indiana Dunes National Park to be temporarily closed.

US Steel said last week that a failure by a vendor to deliver sulfuric acid used for wastewater treatment was the cause of the September 26 outbreak. The EPA said preliminary testing indicated that iron-stained wastewater posed no risk to public health.

The discharge comes weeks after a federal judge approved a revised agreement with the company over the 2017 spill, which occurred when the Portage plant discharged wastewater containing potentially carcinogenic chemicals into the Burns Waterway.

Last week, a coalition of more than 20 local and national entities with interests in the shoreline of Lake Michigan called on Indiana leaders to do more to protect Lake Michigan from industrial sprawl.

“It is clear that Indiana’s system of water pollution control regulation is broken,” he said in his October 1 letter sent to Governor Eric Holcomb.