Abstract: A surface aerator equipped with a central vertical shaft which can be coupled to a drive means, substantially vertical blades being mounted on the lower end of said shaft.According to the invention an upwardly expanding, smooth cone is fitted underneath, and coaxially with, the shaft, the greatest radius of which cone is appreciably greater than the radius of the shaft, but appreciably smaller than the radius of the aerator at the outer edges of the blades, while the upper edge of this cone is adjoined by an overhead vertical cylinder, the successive blades being linked by an outwardly and upwardly inclined, at least substantially flat connecting plate, which is upwardly staggered with respect to the cone.