A dam spillway for the passage of water from a forebay to an afterbay comprises a means for compressing the atmospheric air by the passing water and a floatation chamber connected to said means. The floatation chamber incorporates a froth separating cavity having a lower wall thereof in the form of a smooth concave curve. Accommodated in the upper portion of the froth separating cavity substantially above the water level of the afterbay is a froth remover in the form of a tubular member provided with a longitudinal slot facing the interior of the cavity. Secured on the froth remover is an assembly of water sprinkling froth suppressing sprayers adapted to communicate with the forebay. Connected to the upper portion of the froth remover adjacent to the sprayer assembly are perforated air ducts secured at the bottom of the afterbay.
