Abstract: Various embodiments of a sealing device serve to preclude the passage of water and debris between the conventional gaps in a deck. The water sealing device comprises an elongated member preferably formed of natural rubber with weather and ultraviolet resisting additives, but may be formed alternatively of vinyl or other resilient plastic materials as desired. In each embodiment, the seal has a pair of upwardly extending flanges along the top of each opposed edge. The sealing device fits tightly within the gap between the boards of a deck, preventing the passage of water and/or other debris between the boards. The flanges are biased outwardly, creating a watertight seal between the boards and the sealing device. Further sealing may be provided by the use of an adhesive and/or caulking compound at the time of installation of the seals, as desired.