Osoyoos Lake level returns to IJC Rule Curve following spring freshet and summer snowmelt


Regulation of Osoyoos Lake by the Zosel Dam has resumed now that Osoyoos Lake levels have returned to within the rule curve.

On July 27, the Osoyoos Lake level declined below an elevation of 912 feet (277.97 meters), the upper limit of the rule curve as defined by Condition 7 of the International Joint Commission (IJC) Orders of Approval for Osoyoos Lake (see the blue line in figure 1).      

figure 1 osoyoos lake levels

Figure 1: 2022 Osoyoos Lake levels (solid blue) and the allowable range under the normal rule curve defined by the Orders of Approval for Osoyoos Lake (solid black).

The level of Osoyoos Lake exceeded the rule curve from June 8 to July 27 in response to increased inflow from snowmelt and decreased outflow due to the elevated stage of the Similkameen River during the spring freshet.

Osoyoos Lake crested at an elevation of 912.99 feet (278.28 meters) on June 22. The operators of Zosel Dam (Washington state) remained in compliance with IJC Orders of Approval during the spring freshet by fully opening the gates at Zosel Dam. As such, Osoyoos Lake levels were then controlled by inflows and maximum outflows which were limited by the higher stage of the Similkameen River.      

Please monitor the International Osoyoos Lake Board of Control website for further hydrologic condition updates as the summer progresses.

Real-time Osoyoos Lake levels are available at ijc.org/en/olbc/watershed/levels. Find answers to Frequently Asked Questions at ijc.org/en/olbc/watershed/faq.