Abstract: A dam spillway to pass water over the crest from a forebay into an afterbay comprises a mixing chamber communicating with a diffuser; said mixing chamber has an intake arrangement ensuring formation downstream of the diffuser of a flotation zone with a froth collector installed at the end thereof; said intake arrangement includes a water flow divider, a water breaking grid and air intake ducts, the divider being installed above the chamber and made in the form of a screen composed of chutes; said water breaking grid of the intake arrangement composed of bluff members is provided in the inlet portion of the chamber, whereas the air intake ducts of said intake arrangement are made in a wall of the mixing chamber below the grid in close proximity thereto.