Officials said Monday that they were bringing truckloads of drinking water to the eastern Montana city of Glendive after traces of nearly 190,000 litres of oil that spilled into the Yellowstone River were found in the city's water supply.

State and federal officials said preliminary tests Monday indicated that at least some oil entered the supply for the city of 5,300 people. They stressed they are shipping drinking water as a precaution and do not know yet whether there is any public health threat to residents. They will perform further tests to determine that.

Up to 190,000 litres of oil spilled in the Saturday pipeline accident. Cleanup crews were being hampered by ice that covers most of the river, making it hard to find the oil.

Officials with Bridger Pipeline LLC of Casper, Wyo. have said the break in the approximately 30.5-centimetre steel pipe happened Saturday morning in an area about 14 kilometres upstream from Glendive, a community in east-central Montana near the North Dakota border.

'Oil has made it into the river. We do not know how much at this point.' - Bridger spokesman Bill Salvin

Bridger spokesman Bill Salvin said Monday that the company is confident that no more than 1,200 barrels — or nearly 190,000 litres — of oil spilled during the hour-long breach.

"Oil has made it into the river," Salvin said. "We do not know how much at this point."

An oil sheen has been seen near Sidney, almost 60 river miles downstream from Glendive, said Paul Peronard, the on-scene co-ordinator for the U.S. Environmental Protection Agency.

Booms are being placed in two areas of open water to try and trap oil with another collection site near Crane, which is about 48 kilometres downstream from the spill site.

"We want to put up a backstop so no free oil can get past this location," Peronard said Monday.

But locating the rest of the oil could prove to be difficult because some of it is trapped under the ice that covers much of the river.

"We really can't see it, so we're going to have to hunt and peck through ice to get it out," Peronard said.

Bridger Pipeline crews were still working Monday to determine exactly where the breach occurred.

If it happened on the bank, some of the oil may be trapped in the soil near the river.

"If it happened underneath the river, then it's all in the river," Peronard said.

Water odour reports investigated

Initial water samples taken at the Glendive water treatment facility showed no sign of oil or gas contamination, said Peronard and Dave Parker, spokesman for Gov. Steve Bullock.

Glendive's intake station draws water from about four metres beneath the river surface, while most of the oil was expected to be floating, Peronard said.

Some Glendive-area residents had reported an odour in their water and those reports are being investigated, officials said.

Bullock planned to visit the spill site Monday afternoon, Parker said.

The Poplar Pipeline system runs from Canada to Baker, Mont., and carries crude oil from the Bakken oil producing region in Montana and North Dakota. It remained shut down Monday while crews planned to pump out any remaining oil from the section of the pipeline where the breach occurred.

The pipeline receives oil at the Poplar Station in Roosevelt County, Fisher and Richey Stations in Richland County and at Glendive in Dawson County, all in Montana. It was last inspected in 2012, Salvin said, and is at least 2.4 metres below the Yellowstone River bed where it crosses the river near Glendive.

Bridger Pipeline, a subsidiary of True Cos., also owns and operates the Four Bears Pipeline System in North Dakota along with the Parshall Gathering System and the Powder River System in Wyoming, according to the company's website.