A method of laying underwater pipelines in the bed (3) of a body of water (2), the method including laying an underwater pipeline (4) along a given path (P) on the bed (3) of the body of water (2); breaking up a ground mass along the path (P) to a given depth in the bed (3); and fluidifying the broken ground mass beneath the underwater pipeline (4) to sink the underwater pipeline (4) into the fluidified ground mass.