Fall 2023 Update on Osoyoos Lake Water Levels and Conditions
As of November 1, 2023, the Rule Curve for maximum and minimum Osoyoos Lake levels has changed for the winter period, allowing lake levels to be maintained between 909.0 feet and 911.5 feet until March 1, 2024 (Figure 1).
Figure 1: 2023 Osoyoos Lake Levels (bright green) and allowable range under the normal rule curve defined by the International Joint Commission Orders of Approval for Osoyoos Lake (solid black).
Osoyoos Lake levels remained near the middle of the range of allowable levels defined by the Rule Curve throughout the summer and into autumn. However, since the beginning of October, lake levels have dropped to below the historical mean due to persistently dry conditions throughout the basin. A significant proportion of Osoyoos Lake inflows come from Okanagan Lake outflows, where lake levels have also been below the mean throughout the summer and into autumn (Figure 2). Okanagan lake levels have been decreasing at a rate similar to that of the mean for late summer and autumn.
Figure 2: 2023 (bright green) Okanagan Lake levels and the International Joint Commission Order of Approval drought threshold (dashed red) for June and July.
- The International Osoyoos Lake Board of Control oversees the operation of Zosel Dam to manage water levels in Osoyoos Lake, which crosses the British Columbia-Washington state border.
- This year’s board and public meetings were held on October 4, 2023. The public meeting was well-attended, with more than 20 people joining in-person and online. A recording of the public meeting is featured on the board website at ijc.org/en/olbc.
- Winter 2023-2024 is expected to be an El Niño year, which typically brings warmer temperatures to the region. Effects on precipitation are undetermined.
- Drought levels are currently at Level 2 (adverse impacts unlikely) for the Okanagan basin and Level 4 (adverse impacts likely) for the Similkameen basin. Up-to-date drought information can be found through the British Columbia Drought Information Portal.
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Dr. Andy Long, US Secretary
Martin Suchy, Canadian Secretary