Abstract: In artificial streams, the presence of the predacious fish, Salvelinus fontinalis, was combined with the presence of a potential crayfish competitor in a fractionally factorial design. In this study I attempted to determine how both predation and competition affect three different species of crayfish; Cambarus bartonii, C. sciotensis, and Orconectes spinosus, from two river drainages on opposite sides of the Eastern Continental Divide. In the James river drainage, the presence of the exotic species, O. spinosus, caused the native crayfish, C. bartonii, to shift its microhabitat distribution to shallower and presumably more dangerous water. O. spinosus, significantly reduced its activity during the day, and was opportunistic in its activity to reduce the possibility of predation by the diurnal trout. In the New River Drainage, where the history of the interaction is longer, the two native species C. bartonii and C. sciotensis, did not have significant impacts upon each other in terms of competition. However, C. sciotensis did significantly reduce its activity when the predacious trout was present. The presence of C. bartonii in both drainages allowed for a comparison of two potentially diverging populations. The two populations of C. bartonii responded significantly differently to the presence of S. fontinalis, supporting the hypothesis that these populations may be genetically separated. The absence of a clear pattern in the roles of competition and predation in this system support the complexity of species interactions and the uniqueness of these communities on either side of the Eastern Continental Divide.