Acoustic-tagged juvenile Chinook salmon (Oncorhynchus tshawytscha) detections in Lookout Point Reservoir and downstream in the Middle Fork Willamette River, Oregon, 2023_24

Federally-threatened ago-0 spring Chinook salmon (Oncorhynchus tshawytscha) were acoustic tagged and released near Lookout Point Reservoir to estimate passage and survival during an experimental reservoir drawdown operation that was designed to facilitate downstream passage through two reservoirs and dams. The experimental operation consisted of lowering the water surface elevation of Lookout Point Reservoir on the Middle Fork Willamette River from 823 ft in late August 2023 to 750 ft by early November 2023 and passing water through regulating outlets at Lookout Point Dam. This operation was intended to improve fish passage for juvenile Chinook salmon through Lookout Point Dam. During our study, acoustic-tagged juvenile Chinook salmon produced by Oregon State University's Wild Fish Surrogate Program were released weekly during late August to late October to determine how fish responded to the drawdown. Detection sites were in Lookout Point Reservoir and Dexter Reservoir on the Middle Fork Willamette River; and near the city of Eugene, Oregon, and near Willamette Falls on the Willamette River. Estimates of fish survival through the study area were calculated from the release and detection records and combined with time-varying covariates of Lookout Dam operations and water temperature in Lookout Point Reservoir and the Middle Fork Willamette River.