Lake Diefenbaker is a
reservoir and
bifurcation lake in Southern
Saskatchewan,
Canada. It was formed by the construction of
Gardiner Dam and the
Qu'Appelle River Dam across the
South Saskatchewan and
Qu'Appelle Rivers respectively. Construction began in 1959 and the lake was filled in 1967. The lake is long with approximately of shoreline. It has a maximum depth of , while the water levels regularly fluctuate 3–9 metres (9–27 feet) each year. Lake Diefenbaker provides water for domestic irrigation and town water supplies. The flow of the two rivers is now regulated with a considerable portion of the South Saskatchewan diverted into the Qu'Appelle. Prior to the dams' construction, high water levels in the South Saskatchewan would frequently cause dangerous ice conditions downstream in
Saskatoon while the Qu'Appelle would frequently dry up in the summer months.