A pipeline leak has spilled tens of thousands of gallons of crude oil into a North Dakota creek roughly two and a half hours from Cannon Ball, where protesters are camped out in opposition to the Dakota Access pipeline.

Members of the Standing Rock Sioux and other tribes, as well as environmentalists from around the country, have fought the pipeline project on the grounds that it crosses beneath a lake that provides drinking water to native Americans. They say the route beneath Lake Oahe puts the water source in jeopardy and would destroy sacred land.

North Dakota officials estimate more than 176,000 gallons of crude oil leaked from the Belle Fourche Pipeline into the Ash Coulee Creek. State environmental scientist Bill Suess says a landowner discovered the spill on Dec. 5 near the city of Belfield, which is roughly 150 miles from the epicenter of the Dakota Access pipeline protest camps.

The leak was contained within hours of the its discovery, Wendy Owen, a spokeswoman for Casper, Wyoming-based True Cos., which operates the Belle Fourche pipeline, told CNBC.

It’s not yet clear why electronic monitoring equipment didn’t detect the leak, Owen told the Asssociated Press.

Read more from CNBC.

Featured image courtesy of Getty Images.