From: Tunnell, 1969; Rezak et al., 1985
Seven and One Half Fathom Bank is a small topographic prominence located on the continental shelf of the northwestern Gulf of Mexico. It is 74 km south of the northwestern entrance to Padre Island National Seashore and 3.2 km offshore from Central Padre Island. The reef is an elongate structure with four distinct rises, which are oriented at an approximate 45° to Padre Island. The second rise from the south with a relief of 5.4m is greater in all dimensions than the other three rises. It used to be a freshwater lake during the last ice age when sea level was 350 feet lower. The bank is highly turbid to fairly clear water conditions and lies in an area of converging currents bathed by coastal waters from the more tropical southwestern Gulf in the summer and the northern gulf in the winter. Some molluscs, tropical fishes and invertebrates frequent this bank. There are near-shore oil platforms and jetties in this area. Recreational scuba diving and fishing are common activities.
Seven and One Half Fathom Bank is a small sandstone prominence and is largely covered by mats of tube-building polychaete worms, sponges, ascidians and hydroids. The reef bears an assemblage of molluscs and crustaceans of mixed warm-temperate and tropical affinities and a substantial number of species in common with the south Texas jetties and other near shore banks further north such as Herald Bank off Galveston. Sponges, hydroids, bryozoans and algae have encrusted the upper levels of the reef to such an extent that bare rock is scarcely visible.