Fiberglass mesh enclosures (1 × 1 m2) in a Typha angustifoliaL. marsh were employed to examine the effects of clay additions on theresident macroinvertebrate communities. Total invertebrate density, insectdensity, and number of insect families decreased significantly by 33%,37%, and 17%, respectively, in enclosures receiving sediment. Morespecifically, incoming clay adversely affected densities of Coleoptera larvae,Diptera larvae, Megaloptera larvae, Odonata larvae, Pelecypoda, andGastropoda. Densities of specific families within the Diptera (larvae) andColeoptera were also affected; Dolichopodidae, Stratiomyidae,Hydrophilidae, Tabanidae, Dytiscidae adults, and Scirtidae larvae decreasedsignificantly in numbers in sedimented enclosures. In contrast, the effectof sedimentation on Carabidae (adults and larvae) and Dytiscidae larvaldensities varied significantly with time, whereby densities were higher in thesedimented treatment only for the initial two months of the study. Densities of predator-engulfer, collector-filterer, and scraper feeding groupswere reduced in sedimented plots by 28%, 44%, and 27%,respectively. Significant short- and long-term increases in turbidity andsuspended solids in enclosures treated with clay, as well as sedimentdeposition, were probably responsible for changes in the invertebratecommunities.