River Eku, a water body in Ona-Ara Local Government of Oyo State was studied to assess the impact of dumpsite leachate on the qualities of surface water and sediment of the river. The mean values for dissolved oxygen (DO) (2.3  1.1 mg/L), chemical oxygen demand (COD) (822  658 mg/L), PO4 3-(0.35  0.20 mg/L), SO4 2-(16.45  2.95 mg/L) were reported for the upstream region, while the downstream mean values for the same parameters gave 3.73  0.56 mg/L, 911.75  813.36 mg/L, 0.68  0.42 mg/L, and 26.18  4.46 mg/L respectively. The dumpsite leachate was also analysed for the same parameters as for the water samples. The mean levels of some pollution parameters gave evidence of pollution in River Eku. The results obtained confirmed that the dumpsite leachate was the source of pollutants in the river.