Gardiner Dam, located 25 kilometres north of the Village of Elbow on the South Saskatchewan River, is the principal dam which impounds Lake Diefenbaker. The
Water Security Agency owns Gardiner Dam, and is responsible for its operation and maintenance.
In conjunction with the Qu'Appelle River Dam, the 64-metre tall, 5,000-metre long dam was officially opened on July 21, 1967, as part of Canada's Centennial celebrations. Both dams create Lake Diefenbaker, a 225 kilometer long reservoir with a full supply level of 556.87 metres. More than a third of Saskatchewan’s population depends on Lake Diefenbaker for various purposes including: power generation, irrigation, recreation, wildlife habitat, municipal and/or industrial use.
When the South Saskatchewan River rises due to major rainstorms or rapid snow melt in Alberta, flooding can occur along its length. Lake Diefenbaker is operated to reduce downstream flows thereby reducing and often eliminating flood damages to property and developments which would otherwise occur. The Water Security Agency issues flow advisories to agricultural producers and other users along the system who could suffer damages during periods of high flood waters.
Constructed between September 1958 and October 1968, Gardiner Dam remains one of the largest earthfill dams in the world.