Impact of continual discharge of untreated slaughterhouse wastewater on water quality of the Ikpoba River was investigated from May to October, 1993. Faecal and total coliform bacterial densities as high as 10(7)/100 ml were obtained from 400 m downstream of the waste discharge outfall, compared to 10(4)/100 ml 200 m upstream. Furthermore, the heterotrophic bacterial population of the receiving water was raised from 10(4)/ml to 10(7)/ml after mixing with the slaughterhouse wastewater Six bacterial genera were isolated and characterised as Salmonella, Escherichia, Shigella, Klebsiella, Streptococcus and Staphylococcus. While Salmonella and Escherichia species were frequently isolated from the wastewater and downstream, Salmonella was not detected upstream. The dissolved oxygen content of the receiving river water dropped from 7.2 mg/l to about 2.4 mg/l on mixing with the slaughterhouse wastewater while suspended solids, BOD5, nitrate and phosphate levels increased appreciably. Although an improvement of the water quality was observed some 400 m downstream, probably as a result of self-purification and dilution effects, the slaughterhouse wastewater did not meet FEPA stipulated standards for food processing industries and, therefore, might pose a potential health hazard to the public.