IJC grants temporary operational variance to restore Osoyoos Lake Levels
Low water levels in Osoyoos Lake have exposed the shoreline. Credit: Town of Osoyoos.
Osoyoos lake levels reached historical lows this winter following unusually dry conditions across the region. As a result the International Joint Commission (IJC) has approved a temporary operating variance for Zosel Dam to manage the levels. Washington State’s Department of Ecology (Ecology) - the operator of Zosel Dam – requested the variance which was recommended to the IJC by the International Osoyoos Lake Board of Control (IOLBC). The variance enables Ecology to raise Osoyoos Lake levels to within the normal operating range for the spring, while preserving critical flows for fish.
Managing lake levels during dry conditions
Osoyoos Lake levels have been below normal this winter due to very limited rain and low snowpack. The BC River Forecast Center reported that snowpack in the Okanagan Basin was at 62% of normal on March 1, 2026. Currently, cooler temperatures are slowing snowmelt, and forecasts show no significant precipitation in the near term.
The dry conditions mean that lake operators have limited water available to both raise lake levels and sustain flows in the Okanogan River. Low water levels have limited lake access, with impacts on boating, recreation, and noxious weed control. Outflows from Osoyoos Lake are necessary to prevent desiccation of salmon eggs and to protect Summer Steelhead spawning habitat in the Okanogan River directly below Zosel Dam.
Figure 1: The Town of Osoyoos boat launch is temporarily closed to protect infrastructure during the low lake levels. Credit: Town of Osoyoos.
The IJC’s Orders for Osoyoos Lake establish allowable lake levels throughout the year (Figure 2). Lake levels may be held as low as 909.0 ft through the winter months, then are required to be held above 910.0 ft beginning April 1. Dry conditions have made it challenging for Ecology to raise lake levels to the required level while simultaneously sustaining Washington State’s required downstream flows.
Figure 2: Water year 2026 (bright green) and water year 2025 (dark green) Osoyoos Lake levels, along with allowable range under the normal rule curve defined by the IJC Orders of Approval for Osoyoos Lake (solid black). Expanded drought conditions rule curve (red dashed). For the period of record from 1987-2025, the mean daily lake level is shown as a black line, and the historical gauged minimum, 10th, 25th, 75th, 90th, and historical gauged maximum lake levels are shaded grey (USGS, IOLBC 2026).
Approved variance to restore lake levels
To address this situation, the IJC has authorized a short-term variance effective April 1 through April 30. The variance enables Ecology to raise Osoyoos Lake to within its normal operational bounds while maintaining the minimum flows required for fish in the Okanogan River downstream of Zosel Dam during a year of very dry conditions.
During this period Ecology will work to restore Osoyoos Lake levels as quickly as conditions allow, while avoiding sudden changes in flow that could affect aquatic life or create safety concerns. The upper lake level limits remain in place, ensuring the lake is not raised above normal spring ranges. As under normal operating conditions, the upper limit may only be exceeded during unusually high flows if Zosel Dam passes all possible flow by keeping all gates open. Basin residents should expect to see lake levels continue to trend upwards in the coming weeks.
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 border.
- Annual public board meetings alternate each year between Osoyoos, B.C., and Oroville, WA. The next meeting will be held September 23, 2026, at 6:30-8:00 PM in Oroville, WA.
- To learn more about the board, visit its “Frequently Asked Questions” page.
- Stay in touch and subscribe to receive email news updates from the Osoyoos board.
Contacts
Sarah Dunn, U.S. Secretary
Martin Suchy, Canadian Secretary
To contact the board by email, use the Contact form on the board’s website.
Subscribe to receive updates on hydrologic conditions in Osoyoos Lake, Zosel Dam operations, annual public meetings, and special projects.