Osoyoos Lake Level Rising During Spring Snowmelt

Due to recent snowmelt in the high elevations of the Okanagan and Similkameen watersheds, Osoyoos Lake surpassed the 912.0 feet level (Plot 1) at 03:00 am PDT on May 14, 2020, with lake levels continuing to rise. The Applicant to the IJC Orders of Approval for Osoyoos Lake that operates Zosel Dam remains in compliance with the 2013 Order of Approval (Condition 7 - normal allowable lake levels); since all gates have been fully open since May 11 to allow maximum conveyance of water past Zosel Dam. Osoyoos Lake levels will continue to rise until lake outflows equal those of lake inflows, which is determined by the level of the Similkameen River near its confluence with the Okanogan River and inflow to Osoyoos Lake.

Similkameen River at Nighthawk discharge has increased substantially in the past few weeks (Plot 2). As a result, the Okanogan River between Zosel Dam and confluence of the Similkameen River began to slowly backup. On May 10 and 11 as Similkameen River discharge increased more significantly above 10,000 cfs (Plot 2), the backwater influence became more pronounced. This is evident by the decreased discharge (Plot 3) and increased stage height (Plot 4) of the Okanogan River at Oroville, and the elevation of Osoyoos Lake (Plot 1).