A system for laying an underwater pipeline along a path on a bed of a body of water, the system comprising: - a construction site to form a string of an underwater pipeline by joining together a curved portion and straight pieces of pipe so that the string includes at least one curved portion shaped substantially like a portion of the bed of the water body including an abrupt change in slope; - at least two vessels to transfer, in the body of water , the string from the construction site to a laying site in the body of water and substantially on the vertical of a path along which to lay the string , wherein the two vessels comprise respective winches connected to the opposite ends of the string and respective traction elements configured to be connected to the opposite ends of the string ; - a plurality of floating devices coupled to the string and so as to selectively support and sink the string in the body of water , and progressively lay the string along the path on the bed of the body of water , wherein each floating device is configured to vary its own buoyancy; - a stabilizer device comprising a stay wire that defines a chord of the curved portion and is connected to the string and is configured to prevent deformation of the curved portion of the string ; - a further vessel comprising a further winch connected to the curved portion of the string and a traction element connectable to the curved portion of the string ; and - characterized in that a ROV is connected to the further vessel and configured to control the laying operations of the string on the bed of the body of water , wherein the information transmitted by the ROV enables controlling the steps of laying the string and governing the position of the vessels , the further vessel , the winches , the further winch , and the operations of the floating devices . - a construction site to form a string of an underwater pipeline by joining together a curved portion and straight pieces of pipe so that the string includes at least one curved portion shaped substantially like a portion of the bed of the water body including an abrupt change in slope; - at least two vessels to transfer, in the body of water , the string from the construction site to a laying site in the body of water and substantially on the vertical of a path along which to lay the string , wherein the two vessels comprise respective winches connected to the opposite ends of the string and respective traction elements configured to be connected to the opposite ends of the string ; - a plurality of floating devices coupled to the string and so as to selectively support and sink the string in the body of water , and progressively lay the string along the path on the bed of the body of water , wherein each floating device is configured to vary its own buoyancy; - a stabilizer device comprising a stay wire that defines a chord of the curved portion and is connected to the string and is configured to prevent deformation of the curved portion of the string ; - a further vessel comprising a further winch connected to the curved portion of the string and a traction element connectable to the curved portion of the string ; and - characterized in that a ROV is connected to the further vessel and configured to control the laying operations of the string on the bed of the body of water , wherein the information transmitted by the ROV enables controlling the steps of laying the string and governing the position of the vessels , the further vessel , the winches , the further winch , and the operations of the floating devices . <EOS>