Based on studies conducted in 1987 and 1993, we have determined that the Asiatic clam,Corbicula fluminea, has moved upstream at least 1.2 km/year in a southeastern U.S. blackwater stream. Since these studies were done in a protected area (the Savannah River Site, South Carolina), our data suggest that this was a process unaided by humans. In addition, the upstream movement has been halted by a large, permanent wetland and two culverts. Because the Asiatic clam has not colonized headwater areas, where several wetlands exist, this precludes the aided movement ofC. flumineaby waterfowl. It is possible that fish are partially responsible for dispersingC. fluminea, at least for longer distances. We suggest that unassisted upstream movements may also be an important dispersal mechanism for this species.