Removal of a dam on Maine's Sebasticook River potentially would cause extensive mortality of two state-listed threatened mussel species, the yellow lampmussel (Lampsilis cariosa) and the tidewater mucket (Leptodea ochracea), occurring in the dam's impoundment. We combined qualitative and quantitative surveys to assess population distributions and densities of these species in the impoundment. We also conducted translocation experiments with Passive Integrated Transponder (PIT)-tagged mussels within- and between-waterbodies to determine effects of translocations on mussel survival. Initially, we translocated a co-occurring common species, the eastern lampmussel (Lampsilis radiata radiata), within the impoundment and to two other sites in the watershed to test efficacy of this tagging method. Recaptures improved 40% by combining visual and PIT tag surveys. We repeated this approach with the threatened species, recapturing 71% (L. ochracea) and 88% (L. cariosa) of the tagged mussels translocated in the river. The relocation site proposed by the dam’s owner in the Incidental Take Plan was extensively reconfigured by ice scour, resulting in few recaptures. As a result of our research, we recommended to the state that mussels be translocated to the river's upper impoundment, where tagged mussel survival was greatest, and least habitat alteration is expected with dam removal.