Crews shut down the pipeline Thursday morning and officials are investigating the cause of the leak, which occurred about 3 miles southeast of the town of Amherst, said Brian Walsh, a spokesman for the state's Department of Environment and Natural Resources.
This is the largest Keystone oil spill to date in South Dakota, Walsh said. The leak comes just days before Nebraska officials announce a decision on whether the proposed Keystone XL Pipeline, a sister project, can move forward.
In April 2016, there was a 400-barrel release -- or 16,800 gallons -- with the majority of the oil cleanup completed in two months, Walsh said.
About 5,000 barrels of oil spilled Thursday.
