A surface bypass collector (SBC) system has been identified as a potential means to improve downstream passage of juvenile salmonids through hydroelectric dams, thereby assisting the recovery of endangered salmon populations in the Columbia River basin. During the spring of 1996, 376 juvenile Chinook salmon, 220 hatchery steelhead, and 168 wild steelhead were implanted with radio transmitters and released into Lower Granite Reservoir (Snake River, Washington) to evaluate a prototype SBC at Lower Granite Dam. About 20% of the fish came within 6 m of the SBC. Of these fish, about 45% (which is 9% of all fish detected in the forebay) passed the dam via the SBC. Average flow during the study was relatively high (3,514 ,3/s)compared to previous years (1994, 2,210.4 m3/s; 1995, 2,805.5 m 3/s), and about 3% of the flow passed through the SBC. High flows likely accounted for about 80% of the fish passing the dam through the spillway or turbine intakes. Our results validated the concept of surface bypass; more information is needed, however, to determine how modifications to the SBC or changes in the operation of the powerhouse and spillway might increase the number of juvenile fish passing through the SBC. Because our results revealed species-specific differences in approach to and passage through the SBC, it is important to consider species composition, out-migration life stage, and origin when developing surface bypass systems.