Addu Atoll marks the southern end of the Maldive archipelago. Addu Atoll is long and it is fringed by broad barrier reefs with large islands on its eastern and western sides. Its lagoon has no islands and is relatively open with few shoals in its centre, but having mazes of coral patches close to the NW and NE corners of its encircling reefs in 7 to 10 fathoms (13 to 18 m) of water. The general depths vary from 20 to 25 fathoms (37 to 46 m), with mud and sand at the bottom.