Abstract: One or more vertically oriented cyclones are arranged for treating polluted water by oxygenizing the water and separating polluting particles contained therein. Each cyclone has a conically tapered open-ended elongated chamber having a top and a bottom. The top is exposed to the air and the bottom is submerged below the surface of the water being treated. The cyclone draws water in through a tangential inlet adjacent the bottom end of the cyclone. Upon entering the cyclone the water to be treated is rotationally moved in a spiral upward along the inside surface of the cyclone. A portion of the water being treated exits the top of the cyclone carrying separated polluting particles, while the majority of the water being treated exits the bottom of the cyclone with air entrapped therein.