Osoyoos Lake, which straddles Washington state and British Columbia, is set to rise a month earlier than normal and the Washington Department of Ecology wants residents to be aware.

According to Ecology less than average snow levels are being reported in all watersheds in the region and temperatures are on the rise. Because of this, the agency will raise the lake earlier than usual to avoid water shortages and low flows later in the summer. The goal is to bring the lake to its maximum mandated operational level of 912 feet by early May, rather than by June 1 as usual.

Ecology regulates the lake’s levels by opening or closing gates at Zosel Dam, near Oroville. This is done because of seasonal mandates agreed upon by the International Joint Commission of the Boundary Waters Act between the United States and Canada. The lake serves as a source of water for irrigation and summer recreation in both Okanogan County, Washington, and Osoyoos, British Columbia.

Releases from Okanagan Lake to the north and snowpack runoff in British Columbia can impact lake levels at Osoyoos. And, during the snowpack runoff season, the level of the lake can rise sharply and the lake could rise beyond 913 feet and can reach as high as 915 feet, explained Al Josephy, with Ecology’s Water Resources Program.

“This phenomenon is driven by snowpack and temperatures, and cannot be controlled by Zosel Dam,” said Josephy. “Although the very high levels are rare, we’re reminding lake residents that it can cause inconvenience and occasional flooding to property owners along the lake and down to the site of the dam itself.” 

Lake levels are mandated by the international joint board, made up of representatives from the United States and Canada.