The company building an oil pipeline that has been subject to sustained public protests said on Thursday it has resumed drilling beneath a North Dakota lake despite a last-ditch legal challenge from a Native American tribe leading the opposition.

Energy Transfer Partners LP (ETP.N) is building the $3.8 billion Dakota Access Pipeline (DAPL) to move crude from the Northern Plains to the Gulf of Mexico. The project was put on hold under the administration of former Democratic President Barack Obama, but new President Donald Trump, a Republican, helped put it back on track.

The federal government this week cleared way for the project to resume, leading the Standing Rock Sioux Tribe to file a court challenge on Thursday seeking a temporary restraining order to stop the 1,170-mile (1,885-km) pipeline.

But Energy Transfer Partners said it has begun drilling under Lake Oahe, which is part of the Missouri River system. It expects the Dakota Access Pipeline to begin service in approximately 83 days, according to a company spokeswoman.

Drilling under Lake Oahe will be completed in 60 days, and the company will require another 23 days to fill the pipeline to Patoka, Illinois, the spokeswoman said.

Native American tribes and climate activists have vowed to fight the pipeline, fearing it will desecrate sacred sites and endanger a source of the country's largest drinking water reservoir.

Public opposition has drawn thousands of people to the North Dakota plains, including high-profile political and celebrity supporters. Large protest camps popped up near the site, leading to several violent clashes and some 600 arrests.

Supporters say the pipeline will be a safer mode of transportation for the oil than rail or trucks.

“This administration (Trump's) has expressed utter and complete disregard for not only our treaty and water rights, but the environment as a whole,” the Standing Rock Sioux Tribe said Thursday in a statement on its website.

Legal experts have said the tribe faces long odds in convincing any court to halt work on the pipeline.

To obtain the temporary retraining order, the tribe must convince the judge there will be immediate harm suffered and prove that it has a strong overall case should its suit to halt the project completely go o trial.

(Additional reporting by Daniel Wallis in New York; Writing by Daniel Trotta; Editing by Bernadette Baum and Matthew Lewis)