This paper reports on a study carried out to determine the effectiveness of using a hyper accumulating plant like Eichorneacrassipes (water hyacinth) to reduce toxicity of produced water gotten from an oil field of the Niger Delta region of Nigeria. Results from the phytoremediation experiment showed that the concentration of biological oxygen demand (BOD), chemical oxygen demand (COD), and oil/grease were reduced from initial concentrations of 10.6mg/l, 150 mg/l and 7.70 mg/l to 7.25mg/l, 106.25 mg/l and 8.35mg/l respectively. Heavy metals like iron (Fe), zinc (Zn), Magnesium (Mg), nickel (Ni), copper (Cu), and lead (Pb) were reduced from initial concentrations of 3.00 mg/l, 3.40 mg/l, 1.22 mg/l, 1.40 mg/l, 0.06 mg/l, and 0.030 mg/l to 2.18, 2.09, 0.82, 0.25, 0.015, and 0.009 mg/l, respectively. A comparison of the system’s effluent characteristics with effluent discharge limits in Nigeria, show that for inland, near-shore and offshore disposals, the effluent can be discharged into these environments with minimum public hazards. It is recommended that every company should carryout proper detoxification of produced water before disposal, while regulatory agencies such as DPR, FEPA, etc., must ensure proper monitoring and enforcement of effluent standards.