PIPELINE USED TO carry crude oil is shown at the Superior, Wis., terminal of Enbridge Energy in June 2018. (AP Photo/Jim Mone, file)

MADISON, Wis. (AP) — The state Department of Natural Resources is investigating a possible oil spill near the Bad River Band of Lake Superior Reservation in far northern Wisconsin.

DNR officials said Enbridge Inc. reported Wednesday that a contractor had encountered soil suspected to be contaminated along the company’s Line 5 pipeline south of Ashland about a mile west of the reservation.

Enbridge officials said they couldn’t find a leak in the pipeline and believe the contamination was from a past discharge, according to the DNR. Agency staff have visited the site several times and haven’t detected any additional petroleum odors or soil staining, department officials said.

Line 5 runs from Superior to Sarnia, Ontario, crossing about 12 miles of the Bad River’s reservation. The Canadian oil company is looking to reroute 41 miles of the pipeline south of the reservation after the tribe sued in 2019 to have the section crossing its lands removed.

The DNR is currently finalizing an environmental impact statement for the project. The agency’s draft environmental impact statement drew intense criticism from environmental groups, tribal members and activists who argued it didn’t adequately evaluate impacts, including the risk of spills.

Line 5 also crosses the Upper Peninsula, including parts of Iron and Dickinson counties, and routes underwater across the Straits of Mackinac. Enbridge has proposed establishing an underground tunnel beneath the straits for the pipeline, a plan Gov. Gretchen Whitmer has opposed while seeking to shut down the existing pipeline, citing the environmental risk of a leak in the Great Lakes.