Abstract: Traditional downstream guidance and bypass facilities for anadromous fishes (surface bypasses, surface guidance structures, and behavioral barriers) have typically been ineffective for anguillid eels. Because eels typically spend the majority of their time near the bottom in forebay environments, deep bypass entrance structures with bottom entrances hold some promise for increased effectiveness as protection measures for this species. A new design of deep-entrance bypass system that uses airlift technology (the Conte Airlift Bypass) to induce flow in a bypass pipe was hydraulically and biologically tested in a simulated forebay environment under controlled laboratory conditions. Water velocities of 0.9 to 1.5 m/sec could be generated at the bypass entrance (opening with 0.073 m2 area), with corresponding flows of 0.07 to 0.11 m3/sec. Gas saturation and hydrostatic pressure within the bypass pipe did not vary appreciably from a control (no air) condition under tested airflows. Migratory silver-phase American eels (Anguilla rostrata) tested at night under dark conditions readily located, entered, and passed the bypass; initial avoidance rates (fish avoiding entrainment into the entrance) were lower at higher entrance velocities. Fish that entered the bypass pipe tended to enter headfirst, but those fish that then exited the pipe upstream (rejected the bypass) did so more frequently at lower entrance velocities. Eels appeared to swim against the flow while being transported downstream through the pipe; median transit times for each test velocity ranged from 5.8 to 13.7 sec, with transit time decreasing with increasing entrance velocity. There was no strong avoidance of the vertical section of the pipe which contained injected air. No mortality or injury of bypassed eels was observed, and individual eels repeatedly passed through the bypass at rates of up to 30 passes per hour, suggesting that individuals do not avoid repeated entrainment through the bypass.