Abstract: A water blocking device mainly for the use on the interior of buildings and the like, but also usable outside thereof comprises a triangular-shaped structure in two shapes which may be interlocked to form small dam-like barriers. The primary structure is straight and formed with tongue and groove ends with one tongue being interlockable with the groove of the adjacent section. The second shape being that of a 45.degree. curve again with the tongue and groove interlocking end portions. On the bottom surface of both type sections, recessed disc portions are provided to form in effect a plurality of miniature suction cups. Thus, when two or more of these structures are interlocked together and appropriately fastened to a smooth surface such as provided by a floor of a building, a quickly removable and interchangeable semi-permanent dam structure will be formed.