Downstream passage of outmigrating juvenile salmon (migrants) at hydropower dams on the Columbia and Snake Rivers has, generally, not been entirely successful. To date, research in the region has generated considerable, but often inconclusive, results as to the factors influencing observed migrant guidance and passage. This dissertation synthesizes existing fisheries and sensory biology literature together with fundamentals of fluid mechanics and river hydrogeomorphology to develop a theoretically rigorous hypothesis of observed migrant movement behavior at Lower Granite Dam on the Snake River, Washington USA (chapter 1). The hypothesis, the Strain-Velocity-Pressure (SVP) Hypothesis, is supported by existing 3-D acoustic-tag telemetry data, multi-beam hydroacoustic passage data, 3-D computational fluid dynamics (CFD) modeling, and 3-D spatially­ explicit, time-varying virtual fish simulation that outputs model results in similar form to data collected by field instrumentation.