Cay Sal Bank of the Bahamas, North of Cuba22.9N 77.2W
The bright turquoise form in the sea north of Cuba is caused by the Bahama Banks, the submerged carbonate platforms that make up much of the Bahama Archipelago. The water appears light greenish-blue then suddenly dark blue because the waters above the platforms are shallow, then become very deep where the platforms abruptly drop off.
The bank visible here north of Cuba is the Cay Sal Bank (Spanish: Placer de los Roques), the third largest and westernmost of the Bahama Banks. In a geographical sense, it is separate from the Bahamas proper as it is much closer to Cuba (from which it is separated by Nicholas Channel, at a distance of 50 km) than to the closest Bahamanian island.