Constructed wetlands were studied for treating polluted river water. A three-stage wetland with gravel, zeolite, and fly ash was more effective at removing organics, nitrogen, and phosphorus compared to a single-stage wetland. The three-stage system also reduced ammoniacal odour in the water. Both wetlands performed similarly in removing COD, turbidity, and blue-green algae. The water quality in the area with the wetlands was better than in areas without them, with lower levels of COD, TN, and TP, preventing eutrophication.