Enbridge Inc said on Saturday that it had shut down its 450,000 barrel-per-day (bpd) Alberta Clipper pipeline, the largest source of U.S. oil imports, after an oil spill at a Saskatchewan pump station.

The estimated 125 barrel spill was mostly limited to the Rowatt pump station, located south of Regina, though some windborne oil sprayed onto the property of a nearby landowner, said Enbridge spokesman Graham White.

Enbridge is investigating the cause along with the National Energy Board, said White, noting that the estimated size of the spill is preliminary and could change.