A method of forming artificial reefs in which a set of blocks having internal cavities full of air are interconnected in the desired shape of the artificial reef. The blocks of the set float when full of air and the thus defined reef is towed to the location of use, at which time an air valve in the upper region of each block is opened, permitting the air to escape and sew water to enter the block through an opening in a lower region. In this way the set of blocks is sunk to a designated location on the sea bed adjacent a sandy beach, forming the desired reef. Depending on the configurations of the individual blocks and of the overall shape of the reef, the invention permits both the formation of waves suitable for water sports, such as surf, windsurf and the like, and also the making of an otherwise dangerous beach safe for bathers. The reefs formed in accordance with the methods of this invention may be removed by the simultaneous filling of the blocks with compressed air through the valves and respective openings, thus expelling the sea water from the interior of the blocks which will once more rise to the surface of the sea for towing to another location for dismounting or re-use.