Abstract: This disclosure relates to an underwater excavation apparatus comprising a tube in which a propeller is mounted for rotation. The tips of the propeller blades are formed with jets supplied from a high-pressure water supply through passages in the propeller blades. The jets impinge on vanes mounted on the tube wall around the propeller to cause the propeller to rotate and thereby draw water through the tube from a inlet at one end to an outlet at the other end to act on the seabed. The apparatus is particularly useful for excavating trenches on the seabed and exposing previously covered installations on the seabed.