Abstract: An aerator has a submersible mixing tube having a water inlet and an aerated water outlet. An aspirating tube penetrates the mixing tube between the water inlet and the aerated water outlet, the aspirating tube having an air outlet introducing air into the mixing tube and an air inlet drawing in air from atmosphere above a water surface. The mixing tube has an outboard motor lower unit engagement to engage a lower unit of an outboard motor in use such that a propeller thereof locates entirely within the mixing tube with a midsection of the outboard motor extending from the engagement. As such, the propeller of the outboard motor lower unit thrusts water past the air inlet thereby creating suction at the inlet to draw air via the mixing tube to mix with the water to expel a plume of aerated water.