Adult Pacific lamprey (Lampetra tridentata) encounter various obstacles to upstream migration at Columbia and Snake River hydropower dams. Previous radiotelemetry studies indicate that lamprey have particular difficulty entering fishway entrances and passing through transition areas, past count windows, and in serpentine weir sections of the fish ladders. The primary objectives of the 2007 radiotelemetry study were to: 1. Experimentally evaluate the effects of lowered water velocities at fishway entrances at Bonneville Dam on lamprey behaviour and passage efficiency. 2. Evaluate lamprey passage efficiencies, passage times, fishway entrance use patterns, andfallback at the Bonneville, The Dalles, and John Day dams. 3. Evaluate lamprey behaviours near the Bonneville Dam count windows.