An ankle-foot orthosis which is capable of being worn by a user in an acquatic environment which is lightweight, water-resistant, and reduces the amount of hydrodynamic drag during motion of a leg of a user when in water. The ankle-foot orthosis can be fully customizable to the needs of the user. The ankle-foot orthosis including three protective components； a shank shell, a shin plate, and a foot shell. The ankle-foot orthosis optionally including an additional protective component； a dorsal foot plate. At least one flow passage within each of the shank shell and the foot shell. The at least one flow passage providing water drainage and air ventilation, and reducing the overall weight of the shank shell and foot shell.
