Electronic monitoring equipment failed to detect a pipeline rupture that spewed more than 176,000 gallons of crude oil into a North Dakota creek, according to the pipeline’s operator, about 150 miles from the site of the Standing Rock protests.

The potential for a pipeline leak that might taint drinking water is at the core of the months-long standoff at the Dakota Access pipeline, where thousands of people have been protesting against its construction. That pipeline would cross the Missouri river.