Abstract: A flexible envelope, of fabric, plastic sheet or similar material, is made buoyant by being filled with water of lower salinity than the surrounding medium, and used to lift loads underwater. The lift can be generated in situ by pumping water into the envelope after it has been attached to the load through a hose form the surface, and reduced by either releasing the water from within the envelope or pumping it back to the surface again. By combining these two operations, the lift can be exactly controlled. Several envelopes can be used to lift a single load, and the load itself can be made up of small objects placed in a suitable container by other means. The envelopes may be towed into position, or may be provided with their own means of propulsion.