The heavy oil and diluent leaked from Husky Energy Inc's Saskatchewan Gathering System pipeline on Thursday, flowing into the North Saskatchewan River.
In a telephone conference with reporters, officials from the province of Saskatchewan said they had built five booms to contain the spill and were working with Husky and the federal government on a cleanup plan.
The oil plume had passed the village of Maymont, more than 100 km (62 miles) downstream from where the spill started, said Wes Kotyk, executive director of environment protection with the province.
Husky said the cleanup at the site of the leak had been completed, although neither it nor the province gave a time line for resolving the issue entirely.
The company also said three birds had been "impacted" by the spill and that one died.
It was not immediately clear what caused the spill, which the province said first appeared 300 meters (yards) from the river, a figure revised from an earlier one of 600 meters.
Husky spokesman Mel Duvall said in an email: "We’ll deal with the cause in due course."
Sam Ferris, a provincial water agency official, said the city of North Battleford, upstream from Maymont, had shut its supply intake and switched to using groundwater. But that supply was limited and the city was exploring alternative sources, he said.
Ferris said the city of Prince Albert, farther along the river, was building a temporary pipeline of up to 30 km (19 miles) to draw water from another river.
"It won't work in winter in Saskatchewan, I can guarantee you that," he said.
The province has said it is too early to talk about cleanup costs.
(Reporting by Ethan Lou in Toronto; Editing by Peter Cooney)
By Ethan Lou