Similar to the Oldman River, the St. Mary is host to guides from both Calgary and Fernie. It is a cross-border tributary of the Oldman River, that along with the Belly River and Waterton River, drain a small part of Montana in the US and forms part of the Hudson Bay watershed in Canada. Starting as a stream on Gunsight Mountain in Glacier National Park, the river flows into St. Mary Lake, the second largest in the park. After exiting the park, the river continues through the Lower St. Mary Lake, then through the St Mary Reservoir and eventually empties into the Oldman River in Alberta.

Suffering from mining related pollution in the 1970’s, the tailings have since been diverted and the river today is in fine condition. As a fly fishing only river, it’s one to float since it is only possible to wade across during the lowest levels of the season. A variety of fish call St Mary home, including whitefish, suckers, dolly varden, burbot and Yellowstone cutthroat. Cutthroat here are known for their naiveté – reputed to be very numerous and quite easy to catch.