Just about any underwater structure attracts fish - especially off of sandy coastlines - because it provides a surface for colonization of algae, grasses, corals, sponges, etc., it provides shelter for small fish to hide in (which attracts the bigger fish), and interestingly, because it provides shade. In coastal counties, volunteer organizations and even local governments actively install fishing reefs for the fishing community.

See http://www.artificialreefs.org for more information on the Reef Ball(TM)