Purpose and Background
The Yakima River Mile 25 Thermal Refuge project is focused on increasing the cool water influence of a disconnected oxbow on the left bank of the Yakima River near Benton City. The goal of the project is to provide a refuge area for migrating adults and improve rearing conditions for juvenile salmonids. This project, coupled with several other in development projects downstream of this location, will capitalize on critical sources of cool water in this very hot portion of the Yakima River. This project is made possible through the generosity of a volunteer landowner.
Implementation
During the summer of 2019, project partners excavated an alcove at the downstream end of the oxbow (pictured above). The goal was to move the cooler spring groundwater concentrated in the oxbow into the alcove to provide a cool water refuge for adult salmon as they migrate up the warmer reaches of the lower Yakima River. Large wood was added to the alcove, conditions created to restore fish passage to the downstream end of the oxbow channel, and the channel was planted to protect the cool water.
The project area also included an adjacent northerly side channel that is fully-connected to the river but is impacted by sediment accumulation and Water stargrass colonization. The side channel, oxbow, and springs were included in the description of river features identified as high priorities for enhancement in the Assessment of the Lower Yakima River in Benton County, Washington (Appel et al. 2011).
Fish Monitoring
To document use of the alcove by native fish we worked Yakama Nation Fisheries to develop a PIT tag monitoring site at RM 25 during 2021. This monitoring site will make use of the thousands of Yakima basin salmonids implanted each year with passive integrated transponders (PIT tag) by other monitoring projects. If one of these tagged fish enters the alcove their tag will be read by one of the two arrays installed within the alcove. When a tagged salmonid registers on either array its time/date stamp is then stored on a data logger.
The use of two arrays is crucial to gain a better understanding of how fish are using the alcove. Each array can pick up a PIT tag that comes within 8 inches of it. If a fish is detected on only the first array (red) investigators can assume it passed by the alcove however it cannot be said that they utilized the alcove for any great length of time. If a tagged fish registers on both arrays it demonstrates definitively that the fish utilized the alcove. Additionally, when a tagged fish registers on the array, that information is recorded with a time and date stamp so it will be possible to estimate how long a tagged fish remained in the alcove. This site will be monitored for 12 months and the results will help fisheries organizations better understand how fish use thermal refuge project.
Click here for recent update photos: February 2020 Project Update Photos.
Project Partners
The project was funded with support from the McNary Mitigation Fund, WA Department of Ecology’s Husseman Fund, the WA Association of Conservation District’s Voluntary Stewardship Program, the Yakima Basin Integrated Plan, and Regional Fisheries Enhancement Group funds.