The small island cays and the prominent tidal channels cutting between them in the Bahamas can be seen in this photograph provided by Nasa.

An astronaut aboard the International Space Station took this photograph in July.

For astronauts, this is one of the most recognisable points on the planet. The string of cays - stretching 14.24km in this image - extends west from Great Exuma Island.

Exuma is rich with privately owned cays and pirate history. In particular, it is associated with the notorious 17th-century pirate, Captain Kidd.

Small tidal changes on the banks cause great quantities of water to flow daily through the narrow channels between the cays, first in one direction and then the other.

The darker blue sections are the deepest parts of the channels, where the water flow has cut through the rock ridge that makes the line of cays. The surrounding water is shallow - less than 25m - and appears light blue.