One of the greatest challenges posed by environmental risks to aquatic lives in the Niger Delta region of Nigeria results from the indiscriminate discharge of produced water from oil and gas exploration activities in the area into the environment. In this study, Clarias gariepinus juveniles (measuring 17±1.0 cm and mean weight 12.4±0.5 g) were exposed to different concentrations of produced water under laboratory conditions to determine the 96 h LC50 value. The acute toxicity of exposed juveniles was found to be 3.31 ml/L with lower and upper confidence limits of 2.14 ml/L and 3.10 ml/L respectively. Juveniles showed abnormal behaviours, including erratic swimming, restlessness, loss of balance, respiratory distress and death. The degrees of the observed abnormalities were directly proportional to the produced water concentration.