The St. Regis River is an approximately 32.5-mile (52.3 km) 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 330 square miles (850 km). 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.

• List of rivers of Montana
• Montana Stream Access Law