A study of the physico-chemical parameters on surface water of Ona River at Apata, South west, Oyo State, Nigeria was conducted from October, 2010 to March, 2011. Surface water was collected from five different stations along the river. The mean value of surface water temperature was 26.88±0.48oC; water velocity, 0.24±0.07m/s; pH, 7.38±0.09; Total hardness, 109.96±9.06mg/L; Dissolved oxygen, 2.80±0.50mg/L; Biochemical oxygen demand, 405.57±59.47mg/L; Alkalinity, 77.5±5.94mg/L; Free carbondioxide, 63.77±3.19mg/L; Conductivity, 288.76±11.00mg/L; Ammonium-nitrogen, 0.12±0.02mg/L; Total dissolved solids, 554.39±49.9mg/L; Total suspended solid, 1183.65±54.33mg/L. There were significant differences (p<0.05) in the mean values of dissolved oxygen, Biochemical oxygen demand and total dissolved solid with sampling stations. The physico-chemical parameters analysized during the study period showed that Ona river water was not fit for drinking when compared with the acceptable standards of Federal Ministry of Environment, Nigeria.
