The leak occurred on Thursday, the regulator said, and the company was still working on Monday to isolate the oil, which leaked into Coxhill Creek west of Calgary, Alberta's biggest city.
The spill did not affect wildlife, the agency said.
Husky confirmed the incident and said there was no flowing water at the location.
"It is a relatively small area of operations and the spill was light oil," company spokesman Mel Duvall said, adding that cleanup efforts were underway.
Last summer, Husky indefinitely closed a pipeline that leaked oil into a major Canadian river. The incident was the third in the same area in eight months, according to government records.
(Reporting by Ethan Lou in Calgary, Alberta and Apeksha Nair in Bengaluru; Editing by Chizu Nomiyama)