This study evaluated the macro-invertebrate fauna in water bodies of southern Nigeria spanning the rainforest and derived savanna ecozones. The benthic macro-invertebrate fauna of Edo Ecozone comprises 55 taxa, belonging to 13 major groups. The abundance of major taxonomic groups varied considerably among the surveyed aquatic ecosystems. Chironomidae (Diptera) were well represented and dominant in 11 of the 20 water bodies surveyed. Most rare and restricted species were gastropods (Mollusca), one such species, Mutela cf. dibia, being endemic to the catchment. The overall abundance was maximal (97) at Okomu River in the lowland forest and minimal (5) at Avielle River in derived savanna, respectively. The human impact on macro-invertebrate biodiversity is documented, including changes in benthic fauna distribution patterns.