The discovery of an oil pipeline spill earlier this month in western North Dakota has drawn heightened attention because of the battle over the Dakota Access oil pipeline being built about 150 miles to the southeast.

While the spill was on a different pipeline, the Standing Rock Sioux and its supporters say a spill on the Dakota Access pipeline could threaten the tribe's drinking water, which is drawn from the Missouri River.

The developer of the Dakota Access project, Energy Transfer Partners, and the Army are battling in court over permission for the pipeline to cross under Lake Oahe, a Missouri River reservoir in southern North Dakota. It's the last large chunk of construction for the $3.8 billion project to move North Dakota oil 1,200 miles to a shipping point at Patoka, Illinois.

Here are some questions and answers about the spill on the Belle Fourche Pipeline:

How big was the spill?

The pipeline rupture spilled about 176,000 gallons of oil, about 130,000 gallons of which flowed into Ash Coulee Creek. The spill went about 5 f miles down the creek, which feeds into the Little Missouri River, a tributary of the Missouri River. A photo released by the North Dakota Department of health shows the creek with a brown muck on it. Another photo shows what appears to be the pipeline break with oil oozing out.

As of Wednesday, about 46,000 gallons had been recovered. It appears no oil got into the Little Missouri, and no drinking water sources were threatened, according to Bill Suess, an environmental scientist with the North Dakota Health Department. The creek was free-flowing when the spill occurred but has since frozen over.

The spill was in a remote area of the southwest part of the state, far from any major population centers. It fouled an unknown amount of private and U.S. Forest Service land along the waterway.

Dozens of workers have been at the site the past week in subzero temperatures cleaning the spill, which regulators don't expect to be completed until spring.

How was the spill discovered?

A landowner spotted the spill about 16 miles northwest of the town of Belfield on Dec. 5.

Electronic monitoring equipment failed to detect the rupture, but it's not clear why, according to Wendy Owen, a spokeswoman for Casper, Wyoming-based True Cos., which operates the pipeline.

The pipeline was shut down as soon as the leak was discovered. Owen said erosion of a hillside might have ruptured the pipe, but the cause is still being investigated.

Is this a big spill?

It's sizeable, but there have been much larger oil spills in North Dakota. For example, in September 2013, a Tesoro Corp. pipeline break spilled more than 840,000 gallons of oil into a wheat field near the northwestern town of Tioga. That spill is still being cleaned up.

True Cos. has a history of spills in North Dakota and Montana, including a January 2015 pipeline break into the Yellowstone River. That 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.

Is this pipeline like the Dakota Access Pipeline?

It's much smaller. The 6-inch steel Belle Fourche Pipeline, built in the 1980s, is mostly underground but was built above ground where it crosses Ash Coulee Creek.

It's one of a network of thousands of miles of similar "gathering" pipelines that crisscross western North Dakota's oil patch to pick up oil from wells and carry it to collection points, where it ultimately moves into larger pipelines or railroad tankers destined for refineries across the U.S.

The Dakota Access pipeline is a much larger 30-inch steel "transmission" pipeline that will carry nearly 20 million gallons of North Dakota oil daily through South Dakota and Iowa to a shipping point in Illinois, some 1,200 miles away. It is largely complete except for a segment near the Standing Rock Sioux reservation, where it would be buried 90 to 115 feet below Lake Oahe.

Dallas-based Energy Transfer Partners says the line will have modern leak detection equipment, and that workers monitoring the pipeline remotely in Texas could close valves within three minutes if a breach was detected. The pipeline route skirts the northern edge of the Standing Rock Reservation, which straddles the North Dakota-South Dakota border.

The Standing Rock tribe argues that putting the pipeline under the lake imperils drinking water for more than 8,000 tribal members and millions downstream. ETP and other pipeline advocates maintain that transporting oil through pipelines is safer than shipping it by truck or train.