Abstract: A water jet system for trenching of a cable or a pipe below the floor of a river, lake, gulf or ocean bottom. Two opposed water jet legs are carried on a carriage forward of venturi tubes for disposing of the trenched bottom. The carriage includes a hydraulically powered track system for advancing along the length of the cable or pipeline. The water jets are a plurality of nozzles mounted in a rotating tube at different angular directions. When the nozzle tube rotates within the housing and the nozzles pass by different openings at different heights, the jets' high pressure water shoot forth. The high pressure action of the streams of water loosen the sediment below the floor of the body of water, which is subsequently carried away by air or water action through venturi tubes which are positioned behind the jet legs. The jet legs and carriage are positioned, controlled and powered from a work vessel on the surface of the water.