The Oldman watershed is a large, diverse land and water system in southern Alberta, covering 23,000 km in southwestern Alberta and 2100 km in Montana.
It extends eastward from the forested slopes of the Rocky Mountains, through rangelands in the foothills, dryland and irrigated agricultural plains, to the prairie grasslands.
The Rocky Mountains feed the headwaters of the Oldman mainstream and its tributaries (Crowsnest and Castle rivers, Willow and Pincher creeks), while the headwaters of the Belly, Waterton and St. Mary rivers rise in Montana. The watershed varies greatly, both in terms of the status of the land and water resources and impacts from human activities. In headwater sub-basins, water quantity is adequate, quality is fair to good, and riparian ecosystems are generally healthy. However, as the Oldman River flows east, water quality deteriorates, available water supplies diminish, and there are several issues of concern.