GLENDIVE, Mont. (AP) — Ice is hampering crews working to clean up crude oil that spilled in and near the Yellowstone River in eastern Montana over the weekend.

Bridger Pipeline says it’s confident that no more than 1,200 barrels — or 50,000 gallons — of oil leaked during the hour-long breach Saturday about 9 miles upstream from the city of Glendive. A company spokesman says oil has made it into the river, but it’s unclear how much.

The Environmental Protection Agency says an oil sheen has been seen some 60 miles downstream from Glendive.

Booms are being placed in two areas of open water to try and trap oil with another collection site about 30 miles downstream from the spill site.

The EPA’s on-site coordinator says some of the oil is trapped under ice that’s covering the river and locating it could prove difficult.