The Houtman Abrolhos is made up of three island groups, the Wallabi Group, Easter Group and Pelsaert Group.
The most northerly group, the Wallabi Group, consists of an island clump about 17 kilometres (10 mi) by 10 kilometres (6 mi), and also takes in the outlying North Island, located 14 kilometres to the northwest. The main islands of the Wallabi Group are North Island, West Wallabi Island, East Wallabi Island and Beacon Island.[3] The group is best known for the shipwreck of the Batavia on Morning Reef near Beacon Island in 1629,[4] and the subsequent mutiny and massacre that took place among the marooned survivors.[5]
The Easter Group lies to the southeast of the Wallabi Group, from which it is separated by a 9 kilometres (5 mi) wide channel named Middle Channel. It is about 20 kilometres by 12 kilometres, and consists of a number of islands including Rat Island, Wooded Island, Morley Island, Suomi Island and Alexander Island.
Further to the southeast, across Zeewijk Channel, lies the Pelsaert Group, the most southerly true coral reef in the Indian Ocean. The main islands of this group are Middle Island, Square Island, Long Island, Pelsaert Island, Basile Island and the Mangrove Group. A great many ships have been wrecked in the Pelsaert Group, most notably the Zeewijk, which was wrecked on the Half Moon Reef in 1727, the survivors staying on Gun Island for some time afterwards.[6] Other wrecks include the Ocean Queen, wrecked on the Half Moon Reef in 1842; the Ben Ledi, wrecked off Pelsaert Island in 1879; and the Windsor, wrecked on the Half Moon Reef in 1908.[7]