Colvocoresses Reef
Seychelles
Colvocoresses Reef is a wholly submerged atoll in the Indian Ocean. It is located in the northeastern part of the Chagos Archipelago, near Speakers Bank and Blenheim Reef. The reef is 8 km long, and measures 1 to 2 km across. Breakers are visible only during heavy seas.
Data from Wikidata (CC0). Summary from Wikipedia (CC BY-SA).