SUMMARY. Within the past 10 years the introduced exotic bivalve, Corbicula fluminea, has spread from the Savannah River through a riverine swamp into a third‐order blackwater tributary on the Savannah River Site (SRS). We examined the effects of this invasion on a native bivalve, Elliptio cornplanata, and on seston concentration in the stream. Corbicula fluminea has not yet colonized the entire stream and its distribution limit is coincident with the occurrence of gravel beds. Corbicula fluminea appears to cause localized reduction of seston concentration and may rapidly clear the sediment boundary layer of food. There was no evidence of a negative impact on the distribution of the native bivalve in spite of high measured rates of water clearance by C. fluminea.