| St. Mary River | |
| Subdivision Type1: | Country |
| Subdivision Name1: | Canada |
| Subdivision Type2: | Province |
| Subdivision Name2: | British Columbia |
| Subdivision Type3: | District |
| Subdivision Name3: | Kootenay Land District |
| Source1: | Purcell Wilderness Conservancy |
| Source1 Location: | Purcell Mountains |
| Source1 Coordinates: | 49.9167°N -150°W |
| Mouth: | Kootenay River |
| Mouth Location: | Fort Steele |
| Mouth Coordinates: | 49.6167°N -154°W |
The St. Mary River (sometimes represented as the St. Mary's River) is a river in the East Kootenay region of British Columbia. It rises in the Purcell Mountains and flows in a generally southeasterly direction to its confluence with the Kootenay River at Fort Steele, British Columbia.[1]