It flows roughly west to east from the Rocky Mountains, through the communities of Fort Macleod, Lethbridge, and on to Grassy Lake, where it joins the Bow River to form the South Saskatchewan River, which eventually drains into the Hudson Bay.

The Piikani activist Milton Born With A Tooth had attempted to divert the Oldman River away from the Lethbridge Northern Irrigation District canal intake.

[4] The dam was constructed where the Oldman, Crowsnest, and Castle river systems converge.

A dozen municipalities in Southern Alberta declared local states of emergency on June 21 as water levels rose and numerous communities were placed under evacuation orders.

The river and some of its tributaries have formed coulees in Southern Alberta, and the strata revealed by these formations guide local prospectors to ammolite deposits.