In this study, the potential toxicity of process wastewater from oil and gas exploration in the Niger Delta region of Nigeria was investigated on Clarias gariepinus juveniles using a renewable static bioassay with continuous aeration to determine its acute toxicity. Physicochemical analysis of the wastewater showed that it characterised by a foul odour, was slightly alkaline (pH 7.72) and had high values of chemical oxygen demand (COD) and conductivity (100.20 mg/L and 2793.33 ?S/cm) respectively. Lead, chromium and nickel were present at amounts above national (FEPA, NESREA) and international (USEPA) set limits for effluent discharge. The LC50 value obtained for the fish juveniles exposed to various concentrations of the wastewater for 96 hrs under laboratory conditions was 4.45 ml/L with lower and upper limits being 4.11 ml/L and 7.847 ml/L respectively. Toxicosis symptoms observed includes loss of balance, respiratory distress, vertical and erratic movement and death. The fishes were exposed to 2.0, 4.0, 6.0, 8.0, and 10 ml/L (v/v; wastewater/tap water) for 28 days to evaluate the genotoxic effect of the wastewater using the micronucleus test on peripheral blood erythrocytes. The process wastewater induced significant (p<0.05) concentration-dependent increase in micronuclei, binucleated, notched nuclei and immature erythrocytes in C. gariepinus which were considered as cytogenetic damage indicators. Results of this study showed that the tested wastewater was a potential cyto-genotoxic agent and could induce adverse health effects in exposed individuals.