This study was undertaken to assess the effectiveness of implanted substrates in sampling aquatic macroinvertebrate assemblages associated with stone dikes on the Lower Mississippi River and to obtain basic information on assemblage composition, structure, and patterns of distribution over a dike. For study purposes, stone-filled baskets were implanted into a dike near Vicksburg, Mississippi, in February 1979, and retrieved four months later. The resulting data indicated the presence of a diverse and productive assemblage (38 taxa; average of 101,968 organisms/m²), characterized by net-spinning caddisflies, tube-building chironomids, isopods, and clinging mayflies. The caddisfly, Hydropsyche spp., accounted for over 60 percent of the total organisms collected. A comparison of assemblage data obtained from the surface stones of the implanted substrates with data obtained from adjacent surface stones of the dike indicated close agreement in estimates of both assemblage composition and structure. However, on an average basis, over seventy percent of the total organisms collected in the substrate implants were found below the surface layer of substrate. The importance of this finding to future sampling efforts is discussed. Statistically significant differences in assemblage estimates were encountered over both the length and width of the structure sampled. These findings are discussed both in terms of their potential ecological significance and in terms of future sampling design considerations. / Master of Science