Abstract: An underwater paving machine for making fillings on the river beds is provided comprising a boat having a platform carrying a working structure comprising a pair of uprights supporting a horizontal shaft driven by a motor and carrying a number of spools on which rolls of cables or wires are wound. Said cables or wires are intended to carry blocks made of vibrated concrete and initially supported by a cage intended to be anchored on the river bed. The cage with the blocks are sinked into the water so as to form the fillings on the river bed. The tension of cables or wires is controlled by independent clutches associated to the spools. The blocks are coupled to each other by fastening means both in horizontal and vertical directions. In the area of the boat mounting the working structure an enlargement of the hull is provided intended to increase the buoyancy of the boat. A pair of lateral tanks serve to stabilize the boat on the sides thereof.