Spring is here, river flows and lake levels increasing


The spring freshet in the Okanagan/Okanogan and Similkameen basins has begun as temperatures increase. The snow pillow gauges at Blackwall Peak in the Similkameen Basin (elevation 1,940 m) and Mission Creek in the Okanagan Basin (elevation 1,780 m) are near their annual peak and are both currently reporting above normal snowpacks. As winter snowpacks start to melt, river flows are increasing and lake levels are starting to rise. Recent warm temperatures are forecasted for the next week and runoff from the melting snowpack is expected to continue.

The Similkameen River at Nighthawk discharge has increased substantially in the past 5 days (Figure 1), with flows increasing from ~ 1,500 ft3/s (42 m3/s) to 5,880 ft3/s (166 m3/s) currently. At high flows during the spring freshet, the level of the Similkameen River can limit outflow from Osoyoos Lake and create a backwater that causes the level of Osoyoos Lake to rise. Inflow to Osoyoos Lake is determined by the Okanagan River, which is largely controlled by outflow from Okanagan Lake. At present, operations at Okanagan Lake Dam at Penticton have not increased outflow but the level of Okanagan Lake has started to rise in the past week due to the freshet.

Osoyoos Lake levels (Figure 2) have been rising steadily since mid-March, and are currently 910.77 ft (277.60 m). The Applicant (Washington Department of Ecology) that operates Zosel Dam remains in compliance with the 2013 Order of Approval (Condition 7 - normal allowable lake levels). Flows in the Okanogan River at Oroville, which represent outflows from Osoyoos Lake, have started to increase in the past week, but are not yet representative of full freshet conditions.

Please monitor this site for additional news releases in the coming weeks as snowmelt and river conditions change due to rising temperatures.

Real-time Osoyoos lake levels are available on the IOLBC’s website at http://www.ijc.org/en_/iolbc



Osoyoos Lake Levels and range of allowable lake levels under IJC Orders for Osoyoos Lake
Figure 2. 2021 Osoyoos Lake Levels and range of allowable lake levels under IJC Orders for Osoyoos Lake.