The presence of shipworms (Bankia setacea) in Steveston Cannery Basin in the Fraser River estuary is attributed to sea water intrusion. River discharge, tides, geometry of the river channel and basin, and density of the intruding sea water are factors affecting intrusion, which in turn influence larval settlement. Settlement may occur at depths where salinity is less than 15‰ but the larvae fail to survive. However, they will continue to develop where salinity exceeds 20‰. Dredging the channel to a continuous grade would eliminate permanent salt-water "pools" along the bottom and prevent infestation.