The International Osoyoos Lake Board of Control (Board) was established by Order of the International Joint Commission (IJC) dated 12 September 1946 to ensure the implementation of the provisions of that Order relative to the alteration and operation of Zosel Dam. Zosel Dam was built in 1927 on the Okanogan River 2.7 km (1.7 mi) below Osoyoos Lake by the Zosel Lumber Company to create a log storage pond.

Osoyoos Lake straddles the International boundary and is of prime importance to agricultural interests in the Osoyoos, British Columbia and Oroville, Washington region. The lake further serves as a recreational resource and domestic water supply. Physically, the lake is long and narrow with a perimeter of 19 km (30 mi). At an elevation of 911 ft (U.S. Geological Survey datum), Osoyoos Lake covers 23.2 km2 (5729 ac) and contains 325,000,000 m3 (263,500 ac-ft) of water. Whereas the maximum depth is 64 m (210 ft), the mean is only 14 m (46 ft).

In 1980 the State of Washington sought the Commission’s approval to construct works replacing the deteriorating control structure regulating the levels of Osoyoos Lake. The old structure (Zosel dam) had been approved by the Commission in 1947 and operated under the supervision of the Commission’s International Osoyoos Lake Board of Control. The application to replace Zosel dam was approved by the Commission in 1982 followed by a Supplementary Order in 1985 to address certain specific matters including the relocation of the new structure. Construction of the was completed in 1987 with funding provided by the Province of British Columbia and the State of Washington, and the commissioning ceremony for the Zosel (Osoyoos Lake) Dam was held on May 9, 1987. Actual operation of the dam is conducted by the Oroville and Tonasket Irrigation District under contract to the project owner, the State of Washington Department of Ecology (WDOE).

A new International Osoyoos Lake Board of Control was established to supervise the operation of the new structure in compliance with the Commission’s Order of Approval. One of the Board’s responsibilities is to issue drought declarations, and their removal when such criteria, contained in the Orders, are satisfied. Such declarations allows the Lake level to be raised above that for non-drought conditions.

On January 31, 2013, The International Joint Commission announced a Supplementary Order of Approval renewing the State of Washington’s authority to operate Zosel Dam and making minor modifications in how water levels on Osoyoos Lake will be managed.

Supplementary Order of Approval 2013-01-29

The previous rule curve had specified that the lake be maintained within a half-foot range (911.0 to 911.5 feet) from April through October during normal (non-drought) conditions, but be allowed to rise to a maximum of 913.0 feet during drought years.  Following Board recommendations, outcomes of public hearings in Osoyoos and Oroville (July 24 & 25, 2012) and a meeting with the Osoyoos Indian Band (July 25, 2012), the Commissioners decided that the rule curve would include a one foot-range with a 912-foot maximum in the summer under normal conditions, and a two-foot range with a 912.5-foot maximum during drought years.

The International Osoyoos Lake Board of Control holds an annual meeting (including a public meeting) and reports to the Commission each April. Monthly reports of daily lake levels and flows are kept to assure compliance with the Orders.

In September 2015, the International Joint Commission created 4 new Board member positions, for added representation of local community and indigenous knowledge and interests.  This resulted in an expansion of the Board from six to ten members, while maintaining the requirement for equal numbers from both countries.

For more information on the mandate of the International Osoyoos Lake Board of Control, click here for the IJC Directive to the Board.

Orders of Approval