Osoyoos Lake Level on the Rise
The level of Osoyoos Lake has been rising since late April when increasingly warm temperatures began to melt the Okanagan River basin’s deep snowpack, which exceeded 150 percent of normal. Snowmelt has also contributed to high water levels in reservoirs upstream of Osoyoos Lake including Okanagan Lake, which is at its highest level since construction of the current Okanagan Lake Regulation System in the early 1950’s. The persistence of an above normal snowpack coupled with high water levels in upstream reservoirs suggest that higher than normal water levels in Lake Osoyoos may persist through the summer.
An Order of the International Joint Commission (IJC) mandates the range of allowable Osoyoos Lake water levels, which should be maintained when possible between 911 and 912 feet from May 1 to September 15. During normal conditions, Osoyoos Lake levels are regulated at Zosel Dam by the Washington State Department of Ecology, but during periods of high runoff the Order allows for lake levels to exceed this range.
In compliance with the terms of the IJC water management Order for Osoyoos Lake, the gates at Zosel Dam have been fully open since late April to allow for maximum outflow from Osoyoos Lake. With Zosel Dam no longer restricting outflow from the lake, the level of Osoyoos Lake depends on inflow from the Okanagan River upstream and the level of the Similkameen River which, at high flows, can back up water flowing out of Osoyoos Lake.
Inflow to Osoyoos Lake from the Okanagan River is largely controlled by releases from the Okanagan Lake Dam, which are anticipated to remain above normal through the summer due to current inflows to Okanagan Lake, an above normal snowpack in the contributing basin, and the resultant high level of Okanagan Lake. Snowpack in the Similkameen basin is similarly above normal, but flow on the Similkameen River is not regulated by a dam and can increase rapidly in response to warm temperatures and rainfall events.
Since Zosel Dam’s construction in 1987, Osoyoos Lake levels have exceeded 912 feet six times, including reaching as high as 915.09 feet in May 1997. Given that this year’s snow index level for the Okanagan and Similkameen watersheds are 30-40% higher than 1997, it’s possible that water levels on Osoyoos Lake could exceed the high water levels experienced in 1997, depending on persistence of current high temperatures.
The International Osoyoos Lake Board of Control, which implements the IJC’s Order for Osoyoos Lake, will continue to monitor inflows to Osoyoos Lake and flows on the Similkameen River and ensure compliance of Zosel Dam operations with the IJC Order. Real-time lake levels are publically available on the IOLBC’s website at http://www.ijc.org/en_/iolbc.
Chair, Canadian Section
Chair, U.S. Section