Macrobenthic invertebrates’ fauna of Ona River at Apata, Ibadan south-west, Oyo State, Nigeria was conducted from October, 2010 to March, 2011. Benthic samples were collected from five different stations along the river. Three phyla of macrobenthic invertebrates were encountered in the river. They were Arthropoda, represented by three genera, Chironomus (Diptera), Progomphus (Odonata) and Isoperla (Plecoptera); Annelida represented by only one genus, Tubifex (Oligochaeta) and Mollusca represented by six genera of gastropods with four identified species namely, Indoplanobis executus, Melanoides tuberculata, Bulinus globosus, Biomphalaria pfferferi, Lymnaea species and Physa species. Chironomus larvae dominated the macrobenthic invertebrates with a total relative abundance of 59.1% while Isoperla larvae were the least abundant, 0.19% by number. All the macrobenthic invertebrates recorded were pollution-tolerant/Clean water species. The increase in the ecological potential of Ona River throughout the study period was best highlighted by the presence of indicator species.
