Officials in the western U.S. state of Montana say an oil pipeline that ruptured last week dumped about 1,000 barrels of crude oil into the rain-swollen Yellowstone River.

The spill from the ExxonMobil pipeline late Friday near the town of Laurel sent oil many kilometers downstream in the river known for its superb fishing. Residents near the rupture were evacuated as a precautionary measure. The pipeline has been shut down since late last week.

Exxon officials have not said what caused the leak from the 30-centimeter pipeline that runs under the Yellowstone River. But local officials say the river’s high level, the speed of the water and debris may have been factors.

The pipeline originates near the border of Montana and the state of Wyoming. It delivers about 60,000 barrels a day to a refinery next to the Yellowstone River.

ExxonMobil says it is working hard to mitigate the environmental impacts of the spill. The company has fielded a team of at least 200 workers to mop up the oil spill.