The St. Regis River is an approximately tributary of the Clark Fork of the Columbia River in Montana in the United States. It begins at Lookout Pass on the Idaho/Montana border, flowing east and ends at the confluence with the Clark Fork in the town of St. Regis. Its drainage is . The record high flow for the St. Regis River in Montana was recorded on May 19, 1954 at 11,000 cubic feet per second according to USGS gaging data.