AMHERST, S.D. (AP) — TransCanada Corp.'s Keystone pipeline leaked an estimated 210,000 gallons of oil onto agricultural land in northeastern South Dakota, the company and state regulators said Thursday, but state officials don't believe the leak polluted any surface water bodies or drinking water systems.

Crews shut down the pipeline Thursday morning and activated emergency response procedures after a drop in pressure was detected resulting from the leak south of a pump station in Marshall County, TransCanada said in a statement. The cause was being investigated.

Discovery of the leak comes ju...