Colvocoresses Reef is a wholly submerged atoll structure in the Northeast of the Chagos Archipelago, Indian Ocean. It is located 15 km east of Speakers Bank and 28 km northeast of Blenheim Reef. The reef measures 8 km north-south, and is 1 to 2 km wide, with a total area of about 10 km². Breakers are visible only during heavy seas.