Osoyoos Lake Levels to Adjust Due to Dry Conditions
As drought conditions affect the Okanagan/Okanogan and Similkameen Basins in Canada and the U.S., the International Joint Commission (IJC) has approved a request for a temporary variance to how Osoyoos Lake levels are managed this summer. These changes allow the operator of Zosel Dam to hold lake levels within the limits specified under drought conditions in the IJC Order for Osoyoos Lake. The variance will remain in effect from June 20, 2025 until November 1, 2025, or until weather and water supply conditions improve.
Key Changes
The temporary variance allows the operator of Zosel Dam, the Washington State Department of Ecology, more flexibility to operate lake levels than under non-drought conditions. The temporary limits allow Osoyoos Lake levels to range between 910.5 and 912.5 feet, which is an extra half foot above and below the normal summer level range.
Osoyoos Lake Levels this Summer
The operator plans to gradually increase Osoyoos Lake levels during the next few weeks towards the new temporary upper limit of 912.5 feet. The additional stored water will help to augment late summer water supplies and support downstream flows in the Okanogan River, which is crucial for endangered fish and other aquatic species.
Background Information
Osoyoos Lake serves as a source of water for irrigation, fish and wildlife, and summer recreation in both the U.S. and Canada.
The need for the variance in lake levels comes from unusual weather and water conditions the Okanagan and Similkameen basins experienced in early 2025. Normally, Osoyoos Lake levels are kept between 911.5 and 912 feet from May 1 to September 15 in non-drought years. While conditions for a drought year haven't been officially met this year due to proactive water management in the Okanagan Basin, low winter snowpack, coupled with early snowmelt due to warm temperatures, have heightened water supply concerns for the late summer months in the basin.
Okanagan Lake, upstream of Osoyoos Lake, peaked on June 1, 2025, and is being rapidly drawn down, leading to less water flowing into Osoyoos Lake. The Similkameen sub-basin is experiencing significantly reduced flows, at only 47% of normal. British Columbia has reported Drought Level 2 for the Okanagan Basin, and Washington State has declared a drought emergency for Okanogan County, signaling the water stress felt on both sides of the border.
Oversight and Updates
Osoyoos Lake levels are managed by Zosel Dam under the authority of the IJC, which involves equal representation from the U.S. and Canada. Details about the drought and non-drought conditions are outlined in IJC Orders.
For real-time updates on Osoyoos Lake levels, please visit the U.S. Geological Survey web page for Osoyoos Lake.
Contacts
Sarah Dunn, U.S. Secretary
Martin Suchy, Canadian Secretary
International Osoyoos Lake Board of Control
To contact the board by email, use the Contact form on the board’s website.
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