April 19, 2021

Lower Than Normal Water Levels Expected to Continue on Last Mountain Lake

Persistent dry conditions dating back to 2019, combined with below normal snowmelt inflows, are expected to contribute to lower than average water levels on Last Mountain Lake this year.

Levels on Last Mountain Lake are primarily dependent on snowmelt, which was well below normal in 2021, with spring rainfall events typically playing a smaller role.  At current levels, the lake would need above average precipitation this spring to reach near normal levels by the summer.

The elevation of Last Mountain Lake is currently 489.72m, at the lower end of the summer operating range, which spans 489.66 to 490.27m.  Water Security Agency (WSA) is taking steps to mitigate low runoff by increasing releases from Lake Diefenbaker at the Qu’Appelle River Dam to supplement downstream lake levels along the Qu’Appelle chain, including Last Mountain Lake.

WSA anticipates an elevation rise of approximately 15cm by late July as a result of diversions from Lake Diefenbaker.  However, because of upstream conveyance capacity limitations, which are expected to diminish in the summer months due to vegetation growth and upcoming evaporation, Last Mountain Lake is not expected to return to a desired elevation throughout the summer unless well above normal rainfall events are experienced.

In 2020, WSA also diverted water from Lake Diefenbaker to improve downstream lake levels.  However, levels at Last Mountain Lake dropped by about 33 cm from late July to freeze-up in November 2020 because of dry conditions.

WSA understands the importance of recreational lake levels to the public and will continue to utilize the tools within its capacity to manage this situation.

WSA is also continuing to monitor potentially lower than normal water levels at several other lakes and reservoirs in Southern Saskatchewan, including Rafferty Reservoir, Boundary Reservoir, Nickle Lake and Thomson Lake.