McDonald Creek Fish Passage Restoration

The McDonald Creek Fish Passage project will rectify a long-known fish passage barrier and remove sources of fish mortality associated with operation of an irrigation diversion. The project will also improve habitat conditions, sediment, and wood transport in the creek. A small reinforced-concrete irrigation diversion dam with a Denil fishway is located at RM 3.2. Current site conditions are poor. A 2018 barrier assessment by WDFW documented that the dam is a complete barrier to fish and the Denil fishway was only deemed 33% passable for some adult fish. High velocity and turbulence likely make the existing fishway impassable to juveniles. All life stages of ESA-Listed Puget Sound Steelhead, as well as Coho, Cutthroat and Pacific Lamprey will benefit from this project. Improving fish passage will open up 4.5 and 6.1 miles of access to moderate to high quality habitat upstream of the dam for Coho and Steelhead, respectively, resulting in improved spawning and rearing habitat. The project will improve fish passage and enhance conditions for fish and wildlife while also improving Agnew Irrigation Districts ability to divert water according to their water right. This will be achieved by notching the dam, installing a new fish passage structure, and constructing rock weirs and pools below the dam. The existing open diversion canal will be replaced by a buried pipeline with a new head gate and debris rack; and the existing fish screen will be relocated to the new head gate area.

The overall goal of the project is to improve fish passage and reduce fish mortality while maintaining and improving AID’s ability to divert water for irrigation according to their water right. This will be achieved by notching the dam, replacing the Denil fishway with a new fish passage structure for passage during irrigation operations, and constructing rock weirs and pools below the dam for passage outside of irrigation operations. The existing diversion canal will be replaced by a buried pipeline with a new head gate and debris rack; the existing fish screen will be relocated upstream to the new head gate area. ESA-Listed Puget Sound Steelhead, as well as Coho, Cutthroat and Pacific Lamprey will all benefit from this project. Coho and Steelhead spawn and rear both upstream and downstream of the diversion dam. All life stages of the four species will benefit from the project and the benefits will be realized year round. In addition, the project will improve sediment and wood transport through the dam to reduce degradation in downstream reaches and create better fish holding opportunities.