Assessment of water physico-chemical parameters of surface water in a section of the Upper Nun River, around Agbere, Sampou and Odi, in Bayelsa State, Nigeria was carried out. Water samples were collected biweekly in triplicates for three months using water sampling bottles. The physicochemical water quality parameters determined in this study includes Salinity, Electrical Conductivity (EC), Total dissolved solids (TDS), Total suspended solids (TSS), Total alkalinity (TA), Total hardness (TH), Turbidity, pH, Chloride (Cl), Sulfate (SO4), Nitrate (NO3), Iron (Fe), Manganese (Mn), Magnesium (Mg), Bicarbonate (HCO3), Calcium (Ca), Sodium (Na) and Potassium (K). Salinity and pH, were measured in-situ while others were analysed in the laboratory. The study used the Completely Randomized Design. A one-way ANOVA was used to show variance between the means at (P<0.05), using, Statistical package for social sciences software version 25. Result of the study were in ranges; 6.273 – 6.810 (pH), 0 - 0.020 mg/l (Sal), 8.240 – 48.027 uS/cm (EC), 18.720 – 28.360 NTU (Tur), 4.123 – 26.917 mg/l (TDS), 0.08 – 0.54 mg/l (TSS), 0.00 – 1.00 mg/l (HCO3), 0.038 – 0.099 mg/l (SO4), 0.126 – 0.24 mg/l (NO3), 7.33 – 16.33 mg/l (Cl), 3.953 – 8.843 mg/l (Ca), 0.923 – 2.687 mg/l (Mg), 1.647 – 4.437 mg/l (Na), 0.383 – 1.730 mg/l (K), 0.122-0.159 mg/l (Fe), 5.57 – 8.60 mg/l (TA), 10.933 – 18.90 mg/l (TH), 0.010 – 0.021 mg/l (Mn). Conclusively, the water is not in its best quality since some of the parameters surpassed their permissible limits. It is therefore recommend that there should be an alternative source of drinking water for the local people within affected axis of the Nun river. Meanwhile proper refuse disposal methods as well as the discouragement of pier toilets in the water body is advocated.