Mellish Reef, being about 300 km to the east of the Northwestern Group, thus the most distant from the Australian continent of all the reefs and atolls of the Coral Sea Islands Territory, is not considered to be part of any group. It has the outline of a boomerang-shaped platform around 10 km in length and 3 km across, area 25 km2. The surrounding reefs, which enclose a narrow lagoon, are completely submerged at high tide. Near the centre of the lagoon is the only permanent land of the reef - Heralds-Beacon Islet. The island is a small cay measuring 600 m by 120 m, area 57,000 m2, only rising a few ms above the high-water mark