This project involved the installation of a weir in the Okanogan/Similkameen Cross channel to maintain flow in the Okanogan River for Summer/Fall Chinook spawning and summer steelhead spawning.

The Confederated Tribes of the Colville Reservation (CCT) were concerned that wide fluctuations in spring flows in the Okanogan River on the east side of Driscoll Island is detrimentally affecting the spawning and incubation of anadromous summer steelhead and Summer/Fall Chinook. Information suggested that water flow to the east channel of the Okanogan River at Driscoll Island can decrease to levels that are inadequate to support the spawning and incubation of steelhead in that reach, even when substantial flows exist in the mainstem above the bifurcation.

Variability in flows is believed to be caused by morphological changes to the cross section of the channel on the north end of Driscoll Island that connects the Similkameen and Okanogan Rivers which has disproportionately affected the contributions of flow from these two rivers on the flow regime in the mainstem Okanogan River channel on the east side of Driscoll Island. Under low
discharges in the Similkameen River, the existing channels are structured in such a way as to direct the bulk of the Okanogan River flows along the north channel to the Similkameen River. Detrimental effects were documented in 2006 when steelhead redds in this section of the mainstem Okanogan River on the east side of Driscoll Island were dewatered (J. Arterburn Colville Confederated Tribes, Omak, WA, pers. comm.). Also, anecdotal evidence indicated that scouring of the main channel below Zosel Dam occurred at high flow. Importantly, these events occurred during critical periods of spawning and incubation of ESA-listed steelhead, and could
have had substantial negative impacts on production.