A person walks down the sidewalk near the U.S. Supreme Court building in Washington, D.C., U.S., February 16, 2022.
A person walks down the sidewalk near the U.S. Supreme Court building in Washington, D.C., U.S., February 16, 2022. Reuters / JON CHERRY

The U.S. Supreme Court on Tuesday turned away a bid led by Dakota Access oil pipeline operator Energy Transfer LP to avoid additional environmental review of a section that runs under an artificial lake and is opposed by nearby Native American tribes.

The justices left in place a lower court decision that ordered the federal government to undertake a more rigorous environmental study of the pipeline's route underneath Lake Oahe, which straddles the border of North Dakota and South Dakota. The pipeline, which opened in 2017, will continue to operate as the review is carried out.

The Dakota Access pipeline has been the subject of a lengthy court battle between tribes seeking its closure and Dallas-based Energy Transfer.

Whether the project should be shut down was not at issue in Energy Transfer's Supreme Court appeal. But Energy Transfer said in court papers that the pipeline remains "vulnerable to a shutdown" with the new environmental review pending.

The Standing Rock Sioux Tribe, the Yankton Sioux Tribe, the Oglala Sioux Tribe and the Cheyenne River Sioux Tribe have opposed the biggest pipeline out of the Bakken shale basin. The pipeline runs about 1,170 miles (1,885 km) from North Dakota to Illinois. The disputed section on federal property under Lake Oahe, an artificial reservoir on the Missouri River, is 1.7 miles (2.7 km) long.

The tribes draw water from the lake for various purposes, including drinking, and also consider the waters of the Missouri River to be sacred. Their lawyers have said the tribes are worried about a potential oil spill.

The tribes lobbied hard to prevent the easement under the lake from being approved and initially appeared to have succeeded when in 2016 the administration of Democratic former President Barack Obama said it would review its original action to allow construction. But after Republican Donald Trump became president in 2017, the government endorsed the original decision to grant an easement.

Democratic President Joe Biden's administration urged the Supreme Court not to hear the appeal, saying the pipeline operator concerns about a shutdown were overstated.

Washington-based U.S. District Court Judge James Boasberg in 2020 found that the government had violated a law called the National Environmental Policy Act and threw out the approval.

Boasberg ordered a more detailed "environmental impact statement," which is the decision the pipeline operator was challenging. Boasberg subsequently ruled that the pipeline be shut down but the U.S. Court of Appeals for the District of Columbia Circuit blocked that decision while allowing the additional environmental review.

The U.S. Army Corps of Engineers, the federal agency overseeing the permit approval process, has said it expects to complete the review later this year.