Ecology makes seasonal water level changes at Osoyoos Lake

YAKIMA – Water levels in Osoyoos Lake will be lowered over the coming weeks in anticipation of the changing seasons.

The Washington Department of Ecology (Ecology) operates Zosel Dam in Oroville. The dam regulates lake levels at Osoyoos Lake which straddles the border between British Columbia and Washington State. The lake serves as a source of for irrigation and summer recreation in both the U.S. and Canada.

The lake will be gradually lowered to winter operational levels and maintained at about 909.5 feet until spring. Lowering lake levels in the fall provides more storage area for winter rain and melting snow and prevents shoreline damage from winter freezing and flooding. In March, dam operators will raise the lake to the prescribed level of 911.5 feet for summer operations.

As recreational activity on the lake begins to slow down in the fall, Ecology traditionally lowers the level of the lake from its summer (April 1- Oct. 31) levels of 911.5 feet elevation to its winter operational levels of 909.5 feet. These levels are mandated under orders put in place in 1982 by the International Joint Commission (IJC), a board made up of representatives from the United States and Canada.

For more information on the operation of Zosel Dam or Lake Osoyoos, contact Al Josephy at Ecology, (360) 407-6456. To track the progress of lake levels in “real-time,” as well as find additional information, go to the U.S. Geological Survey web page for Osoyoos Lake (

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