(Updates adding clarified timeline of events from Husky)
By Rod Nickel and Nia Williams
WINNIPEG/CALGARY, July 26 (Reuters) - An oil spill into a major Canadian river from a Husky Energy Inc pipeline started late on July 20, but flows were not shut down until the following morning, the company said on Tuesday.
Husky's incident report, released by the Saskatchewan government, said the leak started on July 20 at 8 p.m. CST (0200 GMT) in the western province.
Crews arrived at the site of the Saskatchewan Gathering System pipeline the next morning, Husky executive Al Pate told reporters on a conference call.
Around 1,572 barrels of oil leaked into the North Saskatchewan River, forcing two western Canadian cities to stop drawing drinking water from the river. The 19-year-old pipeline transports heavy oil and helps supply Husky's Lloydminster upgrader.
In a statement released after the conference call, Husky, controlled by Hong Kong billionaire Li Ka-Shing, clarified the sequence of events leading up to the pipeline being shut.
Husky said its monitoring system showed there were pipeline pressure anomalies on the evening of July 20, prompting a review of data and operations. Crews were dispatched along the gathering system that night, but did not identify a leak.
As a precaution Husky decided to start pipeline shutdown procedures around 6 a.m. on July 21, and later that morning received reports of a sheen on the river.
Husky said it activated its emergency response plan, dispatched crews to the site and notified the Saskatchewan government on Thursday morning.
Pate said Husky remains confident that its estimate of the volume of oil that leaked, 250 cubic meters, has not changed.
Farms that rely on city water have been cut off as Prince Albert and North Battleford sought alternate water supply while visits to Saskatchewan Penitentiary, a multi-level security federal prison, were temporarily canceled on Tuesday.
The market impact of the shutdown was likely to be limited because crude can be trucked to a number of other pipeline receipt points on the system, oil market players said.
Husky has declined to comment on whether there had been any impact on production.
In Canada's oil capital, Calgary, some analysts said that although the spill was relatively minor, it would fuel fierce opposition to new Canadian pipelines projects such as TransCanada Corp's Energy East and Kinder Morgan's Trans Mountain expansion.
"It's another incident that anti-pipeline types and environmentalists... will latch on to to say this stuff is dangerous," said Martin King, an analyst at FirstEnergy Capital. (Additional reporting by Catherine Ngai in New York; Editing by Grant McCool and Alan Crosby)