A floating module and fastening system for interconnecting a row of modules while allowing relative movement of the modules resulting from wave action. The present invention provides a system for interconnecting floating structures to form breakwaters and other integrated floating structures. The interconnection system includes one or more cables or other securing lines extending longitudinally through a row of floating structures and fastened at the ends of the row. Two or more socket members, through which the cables pass, are secured in and project outwardly from each end wall of the floating structures. Each of the socket members defines a recess, which extends into the end walls of the floating structures. Opposed socket members projecting from adjacent floating structures are sized so that an end of a first of the socket members fits within an opposed end of a second of the socket members. A resilient member or cushion having a shape generally corresponding to the shape of the recesses in the opposed socket members may be received within adjacent recesses of overlapping first and second socket members.