St. Mary River

The Saint Mary River is a tributary of the Saskatchewan River. The river together with the Belly River and Waterton River drains a small portion of Montana to the Hudson Bay watershed.

The river rises as a stream on Gunsight Mountain in Glacier National Park and flows into Gunsight Lake, then flows into St. Mary Lake, exits the park and flows on into Lower St. Mary Lake in the Blackfeet Indian Reservation. From the reservation, the St. Mary River flows into Alberta and into the St. Mary Reservoir. It flows into the Oldman River which eventually reaches the Saskatchewan River.

It passes near the cities of Cardston, Alberta and Lethbridge, Alberta.

The St. Mary River also provides water for irrigation in Southern Alberta. The St. Mary River Irrigation District (SMRID) is Canada’s largest irrigation district delivering water through 2060 km (1280 miles) of canals and pipelines to approximately 1,505 km² (372,000 acres) of land south of the Oldman and South Saskatchewan Rivers between Lethbridge and Medicine Hat, Alberta.