Half Moon Reef is the outer barrier on the south-western side of the Pelsaert Group, the southernmost group of the Abrolhos. Marine Life Network describes its seaward side as a productive reef with morwong, dhufish, coral trout, groper and kingfish, as well as reef sharks. It is the reef that claimed the Zeewijk in 1727.

The seaward face combines coral and limestone structure with the bigger fish typical of an exposed outer reef. It is dived only on calm days from liveaboards, and pairs with the Zeewijk site and the Pelsaert Drop-off. Little else is published about specific sites along the reef.

The Houtman Abrolhos lie 60-80 km west of Geraldton (about 420 km north of Perth). There is no public accommodation or camping on the islands, so divers visit on liveaboard trips departing Geraldton (a 3-5 hour crossing), on private vessels using the public moorings, or – for snorkelling only – on scenic-flight day tours that land on East Wallabi Island. Half Moon Reef forms the south-western outer edge of the Pelsaert Group, about 70 km from Geraldton.

Dive the seaward face from a tender in calm conditions.

The Abrolhos sit on the edge of the continental shelf in the path of the warm Leeuwin Current, which keeps water at 20-24°C and supports the world's southernmost major coral reefs. The islands are exposed to the south-west swell and to strong southerly winds that blow most afternoons from October to March; the crossing from Geraldton is often rough. Marine Life Network recommends March-May and September-November; late summer-autumn highs give the calmest seas.

Western rock lobster season (15 March-30 June) brings fishing camps and boat traffic. The seaward face is exposed to swell and is diveable only in calm conditions.

Drop onto the seaward reef face at 10-15 m, drift or swim along it looking for pelagics and sharks, and ascend on a DSMB for tender pickup.

Liveaboard only for diving: Image Dive – 'Southern Image', the only dedicated dive boat at the Abrolhos (4 days/4 nights from Geraldton, max 8 divers, 3-4 dives a day); Eco Abrolhos Cruises – 5-day small-group cruises from Geraldton with snorkelling and diving; occasional Perth club charters. Batavia Coast Dive & Watersports (Geraldton) runs Abrolhos trips when boats are available.