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.

Owen said the pipeline was shut down immediately after the leak was discovered. The pipeline is buried on a hill near Ash Coulee creek, and the "hillside sloughed," which may have ruptured the line, she said.

"That is our number one theory, but nothing is definitive," Owen said. "We have several working theories and the investigation is ongoing."

Last week, the Army Corp of Engineers said it would deny Dallas-based Energy Transfer Partners the easement it needs to complete the final stretch of the $3.7 billion Dakota Access pipeline. United States Assistant Secretary of the Army Jo-Ellen Darcy said the best path forward was to explore alternative routes for the pipeline, something Energy Transfer Partners says it will not do.

Energy Transfer Partners says the Dakota Access pipeline would include safeguards such as leak detection equipment and that workers monitoring the pipeline remotely in Texas could close valves within three minutes if a breach is detected.



Republican President-elect Donald Trump has voiced support for the Dakota Access Pipeline. About 5,000 people are still occupying land near the planned construction site.

The 6-inch steel Belle Fourche pipeline is mostly underground but was built above ground where it crosses Ash Coulee Creek, Suess said. Owen said the pipeline was built in the 1980s and is used to gather oil from nearby oil wells to a collection point.



Suess said the spill migrated almost 6 miles from the spill site along Ash Coulee Creek, and it fouled an unknown amount of private and U.S. Forest Service land along the waterway. The creek feeds into the Little Missouri River, but Seuss said it appears no oil got that far and that no drinking water sources were threatened. The creek was free-flowing when the spill occurred but has since frozen over.



About 60 workers were on site Monday, and crews have been averaging about 100 yards daily in their cleanup efforts, he said. Some of the oil remains trapped beneath the frozen creek.

Suess says about 37,000 gallons of oil have been recovered.



"It's going to take some time," Suess said of the cleanup. "Obviously there will be some component of the cleanup that will go toward spring."

True Cos. has a history of oil field–related spills in North Dakota and Montana, including a January 2015 pipeline break into the Yellowstone River. The 32,000-gallon spill temporarily shut down water supplies in the downstream community of Glendive, Montana, after oil was detected in the city's water treatment system.

True Cos. operates at least three pipeline companies with a combined 1,648 miles of line in Montana, North Dakota and Wyoming, according to information the companies submitted to federal regulators. Since 2006, the companies have reported 36 spills totaling 320,000 gallons of petroleum products, most of which was never recovered.

— The Associated Press contributed to this story.

