Fish communities of a river subjected to urban disturbance including a section affected by warm effluents in Southern Nigeria are described. Thirty-nine species were recorded of which 82% occurred upstream, while thermal and downstream sections accounted for 51 and 44% respectively. The species distribution reflected the varying habitat conditions of the three study sections. The fauna upstream was different from those of thermal and downstream sections. The fortnightly occurrence of common species showed the respective preference of freshwater species upstream, and brackish/marine species downstream; the occurrence frequency of some species indicated the influence of warm water in the thermal section. The structure of fish communities in the study stretch is discussed.