An apparatus for constructing sandbags has a movable, floatable platform, and a length of casing disposed in a roll and supported on the platform. The casing has two longitudinal edges and can be unrolled from the roll. There is a hopper for receiving and dispensing a quantity of sand on top of the casing as the casing is unrolled from the roll. The hopper is supported by a crane mounted on the platform, and positioned above the length of casing. There is a device for bringing the longitudinal edges of the casing together after the sand has been deposited, and a stitching machine for stitching the edges of the casing together to form a tube of casing filled with sand. The stitching machine is mounted on the crane above the device for bringing the edges of the casing together. There is a conveyor for conveying the tube away from the stitching machine and off of the platform.