WINNIPEG, Manitoba (Reuters) - A Husky Energy Inc oil spill into a major Canadian river last summer that cut off drinking water supply for two cities was caused by ground movement that buckled a section of pipeline, the company said in a report to the Saskatchewan provincial government.

Husky’s report, which the company made public on Thursday, said the break was not due to material defects, such as corrosion. A supporting report by engineering firm Stantec said heavy rain may have triggered the ground movement.

The spill happened as the Canadian government considers whether to allow oil pipeline projects proposed by Kinder Morgan Inc and TransCanada Corp. Oil pipelines are viewed by the oil-rich provinces of Alberta and Saskatchewan as critical to move crude to tidewater, but they have drawn fierce opposition from environmental and indigenous groups.

The Saskatchewan break, discovered by Husky on July 21, occurred on land about 160 metres (525 feet) from the North Saskatchewan River, and leaked an estimated 225 cubic metres (225,000 litres) of crude oil, the report said. Forty percent of the oil entered the river.

Cleanup operations concluded in October accounted for 210 cubic metres.

The spill forced the cities of Prince Albert and North Battleford to temporarily find alternative sources of drinking water. The province said in September that it had recorded 148 wildlife deaths, including birds and fish.

“We know the impact this incident had on communities and would like to acknowledge the extraordinary assistance we’ve received throughout,” Husky spokesman Mel Duvall said in an email. “From the beginning we have taken full responsibility and continue to do so.”

Husky said it will review leak detection procedures and ensure ground movement risks to pipelines are monitored.

Regulators continue to review the incident.