Figure 1. Map of the Snake River basin, showing locations of major dams and tributaries.

Water temperatures and behaviors of radio-tagged adult Chinook salmon and steelhead were monitored at Ice Harbor (IH), Lower Monumental (LM), Little Goose (LG), and Lower Granite dams in 2000-2003. In all years, cold-water releases from Dworshak Dam on the Clearwater River affected thermal layering in Snake River reservoirs downstream. Large and small color insets are representations of Lower Granite Dam (975 m long, 30 m high), including fishway features typical of the Snake River dams. Colors indicate relatively warm forebay water, cool tailrace water, and intermediate fish ladder water. The fishway is composed of multiple tailrace entrances (white stars) where fish enter collection channels leading under the spillway and/or across the face of the dam. Channels merge at a junction pool and transition area at the base of the pool-and-weir ladder where tailrace water is pumped through diffusers to provide attraction flow at entrances (dark rectangles). The mid portion of the ladder is intermediate in temperature and is a mix of pumped tailrace water and forebay surface water. Dark circles indicate location of temperature loggers and radiotelemetry antennas used to estimate ΔT. BO = Bonneville Dam, TD = The Dalles Dam, JD = John Day Dam, MN = McNary Dam.