A water bath separator includes a tank for receiving a volume of water for forming a water bath having a top water surface and a light material conveyor path extending from the tank such that an upstream end of the light material conveyor path is closely below the top water surface when the tank is in filled operating condition. The light material conveyor path includes a sorting conveyor provided with a row of rotatable, driven shafts mutually spaced in a conveying direction and each extending transversally to that conveying direction. The shafts each carry a row of radially extending impellers for intermittently urging material on the sorting conveyor upward and in conveying direction, the impellers of each of said rows being mutually spaced in longitudinal direction of the respective shaft. The sorting conveyor has an upstream portion located in the tank such that an upstream end of the sorting conveyor is immersed in the water bath when the tank is in filled operating condition.