Osoyoos Lake Levels Adjusted for 2024 Summer Drought: Fall Highlights and Future Outlook
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The International Osoyoos Lake Board of Control monitors hydrologic conditions in the Okanagan/Okanogan and Similkameen basins to inform the management of Osoyoos Lake levels.

Conditions remained dry to very dry in southern British Columbia and northern Washington state throughout the summer of 2024, as reported by the B.C. Drought Information Portal and U.S. Drought Monitor.

In dry years, the International Joint Commission (IJC) allows a wider band of allowable Osoyoos lake levels under the 2013 Supplementary Order of Approval. The wider band affords greater flexibility in lake level management to better meet the demands of ecological stream needs, irrigation and recreational users. 

For Osoyoos Lake, drought conditions are determined by the volume of the flow in the Similkameen River from April 1 to July 31 (condition 8a), the net inflow into Okanagan Lake over the same period (condition 8bi), and the peak Okanagan Lake level in June or July (condition 8bii). 

In 2024, drought condition 8a was met and 8bi was effectively met, while condition 8bii was not met. As such, Osoyoos Lake levels were operated within the wider band as shown by the dashed red line in Figure 1. The Zosel Dam operator remained in compliance with IJC Orders during the period of declared drought, and Osoyoos Lake levels reached a maximum elevation of 912.44 feet (278.1 meters) on June 23, 2024. 

Figure 1. 2023 (dark green) and 2024 (light green) Osoyoos Lake levels, and allowable ranges defined by the IJC Order of Approval for Osoyoos Lake (solid black and dashed red).

 

Okanagan Lake levels were kept high through the spring of 2024 in response to predicted drought conditions in the summer. Peak lake level of Okanagan Lake at Kelowna (WSC 08NM083) occurred on July 5, 2024, at 1122.96 feet (342.28 meters) (Figure 2).  As of November 12, Okanagan Lake elevation is below average at 1121.09 feet (341.71 meters) and is anticipated to continue to decrease through the remainder of the year (Figure 2). 

Figure 2. 2023 (dark green) and 2024 (light green) Okanagan Lake levels, and the International Joint Commission Order of Approval drought threshold (dashed red) for June and July.

 

Looking Ahead

As of November 12, 2024, Osoyoos Lake elevation (USGS 12439000) is below average at 910.53 feet (277.45 meters), while the Similkameen River discharge is also below average at 624 cubic feet per second (17.67 cubic meters per second) (Figure 3). Osoyoos Lake levels are targeted to remain near 910 feet throughout the winter season until the commencement of the snowmelt in March 2025. Until then, the lake operator will continue to balance the lake level with outflows.

Figure 3. The 2023 and 2024 Similkameen River discharge is delineated by the dark blue and lighter blue curves, respectively, compared to historical discharge in gray.

 

Seasonal weather forecasts predict a 60 percent chance of weak La Niña conditions developing in the coming months, which could bring cooler temperatures and more precipitation this winter in the basin. 

Please monitor the Osoyoos Lake Board of Control website for further hydrologic conditions updates as the winter progresses. Real-time Osoyoos Lake levels are provided by the US Geological Survey.

Quick Facts  

  • The International Osoyoos Lake Board of Control oversees the operation of Zosel Dam to manage water levels in Osoyoos Lake, which crosses the British Columbia-Washington state border.   
  • In 2024, Osoyoos Lake was operated under the drought rule curve as defined by the 2013 Order. 
  • To contact the board by email, use the Contact form on the board website.
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