Background and Objective: The water in Niger Delta, Nigeria has significant amounts of iron and manganese. To remove them, a precipitation procedure that involves potassium permanganate is required. In the end, the slush is empty into the aquatic environment without treatment, hence, we investigated the effects of the KMnO 4 , a major water treatment agent on Chrysichthys nigrodigitatus, a dominant freshwater fish in Niger Delta Nigeria. Materials and Methods: Fifteen Chrysichthys nigrodigitatus were self-bred and subjected to one-tenth of the range of KMnO 4 concentrations used for water treatment in Nigeria (0.50, 1.00, 1.50 and 2.00) mg LG 1 and a control. At the end of each experimental period, a fish is removed from each treatment and blood samples are taken from the caudal in anticoagulant-free centrifuge tubes and serum is obtained by centrifugation of blood at 3,000 rpm for 10 min. Similarly, on day 30th, immediately after collection of the blood, a fish from each treatment was dissected and the organs (brain, liver, gills and muscles) were excised, transferred to liquid nitrogen and kept at -25 o C until the analysis. The activities of glutathione s-transferase (GST) and acetylcholinesterase (AChE) in these organs were measured spectrophotometrically. Results: The slight increase in the activity of GST and the decrease in the activity of AChE demonstrated the incapability of the vital organs to neutralize the KMnO 4 generated in the oxidative stress condition and neurological impairment. Conclusion: These studies have proven that KMnO 4 suppresses AChE activity and has a dramatic impact on the antioxidant enzyme in C. nigrodigitatus. Therefore, sludge from water plants should be kept harmless before discharging into the rivers.