After spawning, iteroparous steelhead (Oncorhynchus mykiss) from the Columbia Riverbasin must navigate several hydroelectric dams on their way to the Pacific Ocean. We usedradiotelemetry to investigate migration rates, downstream passage routes, and success of adultsteelhead kelts migrating past lower Snake River and Columbia River dams during the springs of2001 and 2002. Seaward-migrating kelts were collected, radio-tagged, and volitionally releasedfrom the juvenile bypass facilities at Lower Granite Dam (LGR) on the Snake River and atMcNary Dam (McN) and John Day Dam (JDD) on the Columbia River. Migration success rates from LGR to the study area exit (8 km east of Portland, Oregon) were poorer during the low-flownonspill conditions of 2001 (4.1%) than in the more typical flow year of 2002 (15.6%). Keltstagged and released at Columbia River dams had substantially higher migration success thanthose released on the Snake River; 59.6% and 62.3% of the kelts released at McN and 63.6%and 80.0% of those released at JDD were contacted at the study area exit during 2001 and 2002,respectively. Kelt dam passage was predominately via spillways and surface flow routes, andduring periods of spill 90.0% or more kelts typically passed via nonturbine routes. Only 47.2% ofkelts were guided out of turbine intakes by screen systems during nonspill periods. Turbinepassage, the primary alternative route during nonspill periods, may be a substantial source of keltmortality. The poor migration success rate of Snake River kelts in both 2001 and 2002 suggeststhat additional management (i.e. kelt reconditioning, transportation, or both) may be warranted toboost iteroparity rates in this population.