YAKIMA – Water levels in Osoyoos Lake are beginning to rise as the thermometer does the same. The lake straddles the British Columbia and Washington border near Oroville.

Osoyoos Lake is regulated at Zosel Dam at Oroville by the Washington Department of Ecology (Ecology). The lake serves as a source of water for irrigation and summer recreation in both the U.S. and Canada.

During the runoff season the level of the lake can rise sharply. Ecology does all it can do to keep lake levels from rising too precipitously during this period, which can run through early July, but many things are out of the agency’s control, explained Al Josephy, with Ecology’s Office of Columbia River.

Lake Osoyoos is fed from Okanagan Lake and is governed by operational concerns up the Okanagan system in British Columbia. Making room for snow runoff in the upper watershed puts pressure on smaller Lake Osoyoos. Also, water backs up when the much larger Similkameen River joins the Okanogan River below Oroville during spring snowmelt. This makes it impossible to dump water from Lake Osoyoos at the dam, Josephy said.

“When runoff is high throughout the system, dam gates are wide open,” Josephy said. “Even so, there will still be areas of flooding and inconvenience to property owners along the lake and down to the site of the dam itself.”

With adequate snow levels reported in all watersheds in the region, Ecology’s target is to maintain a level of between 911.5 and 912 feet from May 1 to Sept. 15.

“The lake often rises beyond 913 feet and has reached as high as 915 feet, though rarely,” Josephy said. “

Lake levels are mandated by the International Joint Commission (IJC), a board made up of representatives from the United States and Canada. This past winter, new Orders of Control were negotiated to replace 25 year-old orders that expired in February. The new orders provide for a longer period for filling the Lake in the spring.

For more information on the operation of Zosel Dam or Lake Osoyoos, contact Al Josephy at Ecology at (360) 407-6456. Additional information on the International Osoyoos Lake Board of Control and the new Order of Approval can be found at http://ijc.org/boards/iolbc/.

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. For more information on Zosel dam and to see current announcements, see http://www.ecy.wa.gov/programs/wr/dams/zosel.html.