Abstract: The invention relates to a water jet aerator which, in place of conventional metal screens, has at least two separate staircase-like obstacles, which project laterally into the paths of the individual jets and split up the jets, and mix them with air. Several such obstacles are arranged in the immediate proximity of one another, successively in the direction of flow, so that a cohesive, well-ventilated jet is obtained. The configuration of the jet cross-section can vary as a function of the arrangement of the facing walls defining the flow path in the area of the obstacles.