AbstractWe sampled macroinvertebrate assemblages in the littoral benthos and on the surface of snags in the Upper Mississippi, Missouri, and Ohio rivers. Snag assemblages differed from benthic assemblages. Tubificids, Caenis, Tanytarsus, Cryptochironomus, Limnodrilus, and Chironomini were consistently more abundant in the benthos; Nais, Cricotopus/Orthocladius, Nematoda, and Rheotanytarsus were consistently more abundant on snags. Filterers were more abundant and gatherers were less abundant on snags than in the benthos. Snag assemblages differed among rivers and among reaches within rivers. Variation among reaches was the result of direct and indirect effects of high-dam reservoir impoundments (upper vs lower Missouri River) and low-dam impoundment for navigation (impounded vs free-flowing Upper Mississippi River). The maximum relative abundance of filterers in the lower Missouri River, which was the only long unregulated reach we studied, was related to particulate organic C and sestonic chlorophyll a c...