Abstract: A floating aerator that is highly efficient in oxygenating water and wastewater utilizes high-volume, low pressure air that is diffused into a sub-surface oxygen transfer chamber in which water and wastewater is oxygenated. An air lift is created in the oxygen transfer chamber through the discharge of air bubbles in the water column in the aerator. The aerator comprises a floating head having a concave lower surface, a main chamber or barrel that defines the oxygen transfer chamber, and an air diffuser that extends coaxially through the float head and barrel interconnects the float head to the barrel such that there is a discharge slot defined between the lower surface of the float head and the barrel. A ballast ring floats the aerator at the desire level such that a flow of air bubbles and oxygenated water or wastewater are discharged at a subsurface level.