By Don Urquhart, Times Chronicle
The historical low level of Osoyoos Lake won’t see the normal April 1 boost after the announcement today by the International Joint Commission (IJC), which granted a temporary operational variance allowing for lower levels than seasonal norms would enable.
The variance will allow lake levels to be kept at the winter levels for an additional month rather than following the normal requirement for a higher level from April 1, but comes with the added challenge of balancing the diverse needs of water flows and levels on both sides of the border.
The delicate balancing act is a result of Ooyoos lake levels reaching historical lows this winter – down to 909.12 ft (277.1 m) – which is the lowest on record since the dam was built in 1927, following unusually dry conditions across the region marked by very limited rain and below normal snowpack levels. Snowpack levels as of March 1 were estimated at 62 per cent of normal in the Okanagan Basin.
The IJC’s Orders for Osoyoos Lake establish ongoing allowable lake levels throughout the year. Accordingly, levels may be held as low as 909.0 ft (277.06 m) through the winter months, then are required to be held above 910.0 ft (277.37 m) beginning April 1.
“Dry conditions have made it challenging for Ecology (Washington State’s Department of Ecology) to raise lake levels to the required level while simultaneously sustaining Washington State’s required downstream flows,” the statement read.
To address this situation, the short-term variance effective April 1 through April 30 will enable 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.
The International Joint Commission (IJC), which is the international agreement covering the transnational waters of Osoyoos Lake, issued the variance on a request by the Ecology department, which operates the Zosel Dam south of Osoyoos Lake.
This request was based on a recommendation by the International Osoyoos Lake Board of Control (IOLBC), which implements the orders of the IJC and oversees the Zosel Dam operation.
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).
USGS, IOLBC 2026 chart
The dry conditions mean that the Zosel Dam operators have limited water available to both raise lake levels and sustain flows in the Okanogan River in Washington State.
“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,” the IJC said, explaining the conundrum.
In essence, the Ecology department and IOLBC will now tread a fine line of balancing lake levels in an attempt to return it to the normal operating range for the spring, while preserving critical flows for fish.
“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,” it said.
Notably, 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,” it added.
