Abstract: A liquid pump having a rotary impeller of improved construction to eliminate the cavitation in the pump housing. Motor noises are muffled because the exhaust port of the pump is on the heel of the skimmer plate of the pump which is slightly below the water line, allowing the water to act as a muffler. Also, in use of the pump in outboard motors, further efficiency is caused by the Venturi effect created when water passes over the exhaust port. A reverse mechanism is mounted internal to the discharge end of the pump housing to prevent the accumulation of debris on the reverse mechanism. The impeller includes helical blades mounted on an inverted cone. Each blade has an inner peripheral portion near the axial center line of the impeller to present a negative radial rake which decreases as the upper end of the blade is approachable. Each blade has an outer peripheral portion provided with a positive radial rake which increases as the upper end of the blade is approached.