Updated at 8 p.m. ET
TransCanada, the company that owns and operates the Keystone Pipeline, says that an estimated 210,000 gallons, or 5,000 barrels, of oil have spilled near the small town of Amherst, S.D.
The cause of the leak is under investigation, according to the company's website. TransCanada crews detected a drop in pressure at about 6 a.m. CT Thursday morning and shut down the pipeline, which runs from Hardesty, Alberta, to Cushing, Okla., and Wood River/Patoka, Ill.
Amherst is about 200 miles north of Sioux Falls, S.D., and about 25 miles from the state's border with North Dakota.
The conduit is not the controversial and long-delayed Keystone XL Pipeline that TransCanada is still shepherding through the approval process.