A population of shortnose sturgeon (Acipenser brevirostrum) was documentedcongregating at the base of Pinopolis Dam, Cooper River, South Carolina, during the February-March spawning season. Pinopolis Dam is a peaking hydroelectric facility and navigation locklocated within the coastal plane, 77 kin upriver of the mouth of the Cooper River at Charleston.South Carolina. In a 5-year radiotelemetry experiment, shortnose sturgeon did not pass upstreamthrough the navigation lock but congregated at the base of the dam. As a result, a study wasconducted to determine whether the tailrace was used as spawning habitat. The location isatypical of published descriptions of shortnose sturgeon spawning habitat in terms of a suite ofcharacters, including distance upriver, tide, flow characteristics, and substrate. The river is tidallyinfluenced for its entire length, and the bottom substrate in the tailrace is dominated by hard marlwith negligible fine sediments such as silt and sand. Turbine discharge varies from 0 to 329m(3)/S subdaily: current velocities during typical hydroelectric peaking discharge exceed 3 m/s.Egg sampling showed that successful spawning (i.e., fertilized eggs and developing embryos)occurred during the three spawning seasons sampled. Spawning was detected from 27 Februarythrough 29 March 1997-1999) at water temperatures ranging from 11.5degreesC to19.0degreesC (mean = 14.5degreesC), reaching the highest levels published for shortnosesturgeon spawning. Active spawning and lack of upstream passage by shortnose Sturgeon at thissite suggest that physical blockage of migration may prevent fish from reaching preferredspawning habitat, probably to the detriment of the population.