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The majority of the world's large river systems is affected by dams. The influences of unnatural regimes induced by flow management are wide-ranging from both biotic and abiotic standpoints. However, many of these effects are not evident over short (1-2 years) periods (e.g. impacts of annual flow variation). This study examines the long-term effects of annual flow variation on the macroinvertebrate community in the Chattahoochee River (GA) in the reaches below Buford Dam, the major water control structure on the river. Quarterly, macroinvertebrate samples were taken from 2001 to 2011 using Surber and Hester-Dendy plate samplers at six locations spread across 65 km below the dam. Data were analysed via analysis of similarities to determine differences in community composition between high-flow (mean discharge = 58.27 m 3 /s) and low-flow (mean discharge = 26.53 m 3 /s) years. Taxa that contributed most to community differences were determined via similarity percentages analyses and subsequent t-tests. Several insect taxa (e.g. Cheumatopsyche and Ceratopsyche caddisfly larvae, Maccaffertium mayfly nymphs and Taeniopteryx stonefly nymphs) were more prevalent under the high-flow regime. Non-insect macroinvertebrates (e.g. Crangonyx amphipods, Tricladida flatworms and Caecidotea isopods) were more abundant under low-flow conditions. In terms of taxon richness, no significant effects of flow regime were detected. Implications of macroinvertebrate patterns for the fishery and ecological health of the river are discussed.

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