The Oldman River (362 km, mean annual flow rate 95 m3/s), rises near Mount Lyall in the Rockies of southwestern Alberta and flows south then east to join the BOW RIVER and form the South SASKATCHEWAN RIVER in Alberta. The Oldman River's name may come from the Cree term for "old man's playground." It receives tributaries from the US (St Mary River) and WATERTON LAKES NATIONAL PARK. One of few major nonglacial-fed rivers in Alberta, it drains 26 700 km2 of mountains, foothills and prairie. Important as a water supply for FORT MACLEOD and LETHBRIDGE, it has numerous dams and diversions for irrigation in the Lethbridge Irrigation District and St Mary and Milk River developments.

The Oldman River Dam (1991) upstream of Pincher Creek supplies irrigation and municipal water supplies to Lethbridge and adjacent areas of southern Alberta. The dam has aroused considerable controversy, with opponents claiming serious adverse effects on river habitat, archaeological sites and trout fishing. Proponents view the expansion of irrigation development and increased surety of water supplies as benefits that outweigh environmental concerns.