Great barrier reef

 The Great Barrier reef forms very visible light blue arcs in the middle of the dark blue ocean.

The Great Barrier Reef is the world's biggest single structure made by living organisms, composed of over 2,900 individual reefs and 900 islands stretching for over 2,300 kilometres. It is being actively monitored, on the ground and from space, to look for signs of coral bleaching.

The image was taken by Sentinel 2 (Copernicus program) in February 2017.