The South Saskatchewan River Basin is comprised of four major sub-basins: Red Deer River, Bow River, Oldman River, and the South Saskatchewan River. All of the basins begin in the Rocky Mountains and generally flow eastward through the foothills and the prairies. The combined watershed of the basins is 121,095 km2, of which 41% is the Red Deer sub-basin, 22% is the Oldman, 21% is the Bow, and 16% is the South Saskatchewan sub-basin.
The Bow River begins as a mountain stream from Bow Glacier in Banff National Park and winds through the Canadian Rockies, out through Alberta's foothills, through Calgary, and onto the vast prairie. The Bow River joins with the Oldman River to form the main stem of the South Saskatchewan River—and, ultimately, these waters make their way to Hudson's Bay.
- In 2006 the Bow River sub-basin became one of three southern basins to be closed to new water allocations.
- This is the most densely populated watershed in Alberta.