Largest of the Bimini islands in the Bahamas.  The dark blue water is the deep ocean and the lighter area is the shallow water of the Great Bahama Bank.  Image acquired from space in 1984.
NASA/USGS
1984-10-08
<a rel="nofollow" class="external text" href="https://earthexplorer.usgs.gov/">EarthExplorer</a>, USGS