They also said the roughly 2-kilometer- (1.2 mile-) stretch of pipeline, which is owned by Tundra Energy Marketing Inc and feeds into the larger South East Saskatchewan oil gathering system, was exempt from licensing when built in 1968.
It was retroactively licensed by then-owner Enbridge Income Fund Holdings Inc in 2014, the provincial government said, adding that it does not have any record of formal inspection of the line since that time.
Authorities were notified of the leak on Friday, when a member of the Ocean Man First Nation who said he had smelled oil for a week located the spill and alerted the band's chief, who notified Tundra.
Some 180,000 liters of oil have been recovered, along with more than 450 tonnes of contaminated soil, the government said.
Tundra, which is part of Canadian grain trading and energy conglomerate James Richardson and Sons Ltd, is leading the cleanup efforts.
The damaged portion of the pipeline is expected to be removed later on Thursday and sent for further analysis and metallurgic testing.
Provincial officials will investigate the cause of the leak, why it was not detected by the operator, whether the age of the pipeline contributed to its failure, and study the effectiveness of the operators' emergency response.
The spill was discovered just days before U.S. President Donald Trump signed executive orders that will move forward two controversial oil pipelines, including one that will bring oil from the Canadian province of Alberta to the United States. Indigenous and environmental groups oppose the projects.
(Reporting by Alastair Sharp in Toronto; Editing by Paul Simao)
