Water levels in Osoyoos Lake are controlled by a dam in the U.S., south of the Washington State portion of the cross-border lake. (David Wise - Wikimedia Commons)

Water levels in Osoyoos Lake are controlled by a dam in the U.S., south of the Washington State portion of the cross-border lake. (David Wise - Wikimedia Commons)

Fall drawdown at Osoyoos Lake starts

Lakeside residents can expect to see water levels drop six inches over the next week

It’s fall, and the Washington Department of Ecology is drawing down water levels at Osoyoos Lake to winter levels.

Releases from Zosel Dam to the Okanagan River — or the Okanogan River as they call it south of the border — will increase in volume to bring the lake down about two-and-a-half feet from now until December.

A side effect of the extra water that was allowed to build up in the lake this summer, thanks to drought declarations, is a chance to boost streamflows and protect fish species in the river going into the fall, according to Al Josephy, a water resources specialist with the Washington State Department of Ecology. This means the river to the south of Osoyoos Lake will be running high for a while.

“The Okanogan River has a tendency to build up sediments on the riverbed, which, over time, clogs gravels on the bottom, making spawning access for fish problematic,” he said. “Following discussions with local fish biologists, we plan to use the extra available water in the lake to flush those gravels by allowing short intervals of high flows to be released over several days during the middle of September.”

The plan is to ramp up flows to about 1,200 cubic feet per second for one or two days, beginning later in the week of Sept. 16. People living and working along the river below Zosel Dam may experience bursts of high flows and may see conditions like those seen during spring runoff.

Lakeside residents can expect to see the lake drop about six inches sometime between Sept. 17 and 25. Following the flush, the drawdown will proceed in its usual course, and the lake levels will continue to decline. Throughout the year, the Lake Osoyoos Board of Control mandates the cross Canada-United States-border lake levels to meet seasonal needs.

The Zosel Dam, near Oroville, Wa., was built in 1987 as part of the larger Osoyoos Lake International Water Control Structure, a joint venture of the Washington State Department of Ecology and the B.C. Ministry of the Environment.


Steve Kidd
Senior reporter, Penticton Western News
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