The Keystone pipeline has leaked 210,000 gallons of oil in rural South Dakota but officials don’t believe it has polluted water.
The pipeline operator, TransCanada Corp., says it has shut down the system and the state has sent an inspector to the site near the border with North Dakota.
According to U.S. government data, there have been 17 oil leaks in the U.S. larger than the new spill since 2010.
But it comes just four days before Nebraska regulators are due to announce their final decision on whether a major expansion of the pipeline system, called Keystone XL, can pass through the state. The expansion has been fiercely opposed by environmental activists, American Indian tribes and some landowners.
President Donald Trump has approved a permit for the expansion.