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.
The South Saskatchewan Sub-basin starts below the confluence of the Bow and Oldman rivers and drains the area east to Saskatchewan. The main stem of the South Saskatchewan River ultimately makes its way to Hudson Bay.
- In 2006, the South Saskatchewan River Sub-basin became one of three southern basins to be closed to new water allocations.
- The Canadian Forces Base "Suffield" is located in the South Saskatchewan basin.
- Allocations for municipal use are highest in this basin. The town of Bow Island is located in the South Saskatchewan River Basin, yet it draws its water from the Oldman River (678 dam3) through the St. Mary River Irrigation District's infrastructure. The allocation for the City of Medicine Hat is larger than allocations of other cities of similar size because the City has its own power plant which draws water under the municipal licence.
- Municipal allocations of surface water increased substantially between 1970 and 1990 but have remained constant since then.