Osoyoos Lake

Osoyoos Lake Water Levels

Please click here to view the current forecasts of Osoyoos Lake provided by International Joint Commission (IJC).

Osoyoos Lake levels are determined by several factors, including the operation of Zosel Dam in Washington State, the operation of Okanagan Dam in Penticton, stream-flow into Okanagan River between Penticton and Osoyoos, and the flow levels of the Similkameen River, which joins Okanagan River south of the US/Canada border.

The map below provides links to real-time water level gauges in the US and Canada. The BEST gauge for Osoyoos Lake is the US Geological Survey station in Oroville WA. To subscribe to USGS water alerts click here. The system sends out emails or texts about water level changes, and allows users to define when they get alerted.  For example, if your boat will be grounded when the lake reaches 911.5 metres, you can set up an alert for 911.6 metres.  A great free service.

Osoyoos Lake Level Regulation

Osoyoos Lake levels are regulated under the US/Canada Boundaries Waters Treaty, overseen by the International Joint Commission.

The International Osoyoos Lake Board of Control supervises the operations of Zosel Dam by the Oroville and Tonasket Irrigation District, which is under contract to the State of Washington Department of Ecology who owns the dam. The Board of Control holds public meetings each year to answer questions and listen to concerns about lake levels management. The meetings are usually held in early Fall, and alternate between Osoyoos and Oroville. Meetings dates are advertised in local media. For Board of Control contact information click here. Releases from the dam are intended to keep lake levels within a set range. The rules are different for summer and winter, and for "drought years" vs. normal or wet years.

In the winter, the lake is managed in a range between 909.0 and 911.5 feet above sea level. In the summer, the lake is managed between 911.0 and 912.0 in a normal or wet year, and between 910.5 and 912.5 in a drought year.

The actual level of the lake may be anywhere within this range, depending on the flows into the lake, the evaporation and water withdrawals from the lake, and the outflows from the dam.

Mother Nature has the last word, and lake levels may go above the operating range if water is flowing into the lake faster than the dam can release it. Historically, levels have gone above 913 every other year, despite best efforts, and in 1972 the lake peaked above 917. At levels around 913 and above, the water flows right over the dam, without any man-made obstacles.

Another important factor is the Similkameen River, which joins the outflows from Osoyoos Lake when they come together in the U.S. Okanogan River. If the Similkameen is running high, it can slow or stop the outflows, and cause flooding around the lake.

Lake levels may fall below the range if there is a severe drought. There are no requirements for minimum flows to the United States, but the Province of BC tries to maintain flows to protect fish habitat and migrating salmon returning to Canada.

Changes to Lake Level Management

New operating orders for Osoyoos Lake went into effect in 2013. In the summer, the normal operating range used to be 911-911.5 (now: 911-912). During droughts, the target maximum lake level used to be 913 (now: 912.5). The normal operating range in the winter has not changed, but the dam operator is now asked to make a gradual change in lake levels between summer and winter. Changes to the rules for lake level ranges were based on public comment, and environmental needs. There are often differences of opinion, among members of the public on what the best level should be for a given time of year, and these can be different again from the goals of agencies balancing environmental needs with resource demands. The diagram for the lake operation rules is given here, as an Appendix on the final page of the online report.

Osoyoos Lake Water Science Forums

There have been two international forums (2007, 2011 and 2015) on Osoyoos Lake Water Science – covering a range of issues from lake levels to water quality and the health of the fishery. Presentations and reports are available here.

Okanagan Water Information
For information on regional Okanagan Water issues including Eurasian watermilfoil control, visit the Okanagan Basin Water Board website. For information on water conservation, visit the Okanagan WaterWise website. For information about what you can do to prevent harmful zebra and quagga mussel invasions, visit the Don’t Move a Mussel website. To contact the Okanagan Basin Water Board, click here. To learn more about the different types of Algae, review the Algae Identification Field Guide provided by Agriculture and Agri-Food Canada, Agri-Environment Services Branch.

Okanagan Basin Water Board
1450 KLO Road
Kelowna BC V1W 3Z4
(T) 250.469.6323
(F) 250.762.7011
W) www.obwb.ca