About 150 miles from where thousands have protested for months that the Dakota Access pipeline could threaten a Sioux tribe’s water supply, a pipeline in the western part of North Dakota has spilled more than 130,000 gallons of oil into a creek, state officials said.

In all, the Belle Fourche pipeline lost 4,200 barrels of crude oil, or more than 176,000 gallons, before operators shut it down, according to state Department of Health spokeswoman Jennifer Skjod. Most of the oil flowed into the Ash Coulee Creek near Belfield, Skjod said.

It’s unclear what caused the break, according to Wendy Owen, a spokeswoman for Wyoming-based True Companies, which owns the pipeline. A landowner discovered the leak Dec. 5. The company uses monitoring technology designed to detect leaks, but it possibly failed because of “the intermittent nature of the flow” of oil through the pipeline, Owen said.

A blizzard last week has impeded efforts to assess the spill’s extent and its impact on the environment. The creek is frozen. Officials are investigating when the pipeline, which typically carried 1,000 barrels of oil per day, started to leak.

“We have no estimate on when or if it will be operational,” Skjod said of the pipleline.

The Associated Press reported the company has declared 36 other spills since 2006, totaling more than 320,000 gallons of petroleum products.

The area is west of where the Standing Rock Sioux and their allies have fought construction on the Dakota Access pipeline, which had been expected to cross under Lake Oahe, a plan that is now on hold. The Sioux have argued that a pipeline rupture could contaminate the water supply and damage sacred lands.

The Barack Obama administration announced last week that it would not grant an easement to developer Energy Transfer Partners to build the final section of the Dakota Access pipeline. The developer has expressed confidence that the project will be completed after President-elect Donald Trump takes office.