Friday, May 15, 2015

Water levels rising at Lake Osoyoos as
spring snow melt proceeds

by Al Josephy, Water Resources Program, Lacey

Lake Osoyoos (Okanogan County) is beginning to rise as snow melt feeds the lakes and streams in British Columbia, and dam operators in the Province let more water out of Lake Okanagan. Operators at the Zosel Dam in Oroville have been filling Lake Osoyoos from its winter level of 909.5 feet to its usual summer operating level of 911.5.

However, this year Ecology has elected to operate the Lake at closer to 912 feet. Ecology maintains the Lake level in part for water uses below the Canadian border, down the Okanogan River. One of these uses could also include fish passage later in the summer.

In this very unusual water year, with potential for a long, dry summer, storing a bit more water in the freshet is a prudent thing to do.

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

Planning for an unusual summer

Usual spring operations at the dam call for slowly raising the level of the lake from winter operating levels to summer levels between March 1 and June 1 of the year. But 2015 has not played out as a “usual” year. Snow water has been absent this year in most of the Columbia Basin and across the Cascade corridor as well. As a result, many river basins are likely to see drought during the summer.

Lake Osoyoos is fed from Okanagan Lake and is governed under Orders created and overseen by the International Joint Commission (IJC). Lake levels are an integral part of those Orders. Ecology is required to operate the Lake between 911 and 912 feet between June and mid-September. In most years it is convenient for Ecology to maintain approximately 911.5 feet.

For more information on the operation of Zosel Dam or LakeOsoyoos, 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

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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