Barrow Island Marine Park covers the western side of Barrow Island, just south of the Montebellos, and is entirely a sanctuary zone — the highest proportion of no-take area of any WA marine park. It includes Biggada Reef, one of the two significant fringing reefs in the Montebello/Barrow reserve system. From late July, large numbers of green turtles gather in Turtle Bay to breed, and hawksbill and flatback turtles also use the bay.

Barrow Island itself hosts the Gorgon gas project and is a Class A nature reserve; access to Barrow and nearby Boodie, Middle and Double islands is not permitted, and camping is prohibited. DBCA nonetheless notes that visitors can dive, snorkel and swim the reef from vessels. With no operators, it is a private-boat destination only.

About the Montebellos: the group of more than 200 small limestone islands and islets lies 120 km west of Dampier and is protected as the Montebello Islands Marine Park, with more than 150 hard coral species, over 450 fish species, 170 echinoderms and 630 molluscs recorded. Flatback, green and hawksbill turtles nest here, and humpback, minke and Bryde's whales, dolphins and dugong frequent the waters. The islands carry a unique history: British atomic tests were conducted on and near Trimouille and Alpha islands in 1952 (Operation Hurricane) and 1956 (Operation Mosaic), and visitors are advised to visit rather than camp on those islands. Pearl farming has operated in the lagoons since the early 1900s.

Planning notes: Open Water certification is recommended and the site is rated advanced. Expect to spend most of the dive around 8 m, with a maximum of about 15 m. It can only be reached on a multi-day expedition or liveaboard, so it is usually one of several sites dived on the trip and choices are made by the crew on the day. Currents are significant, so timing around the tide is part of the plan. Best season: April–October. Traffic: remote/expedition only.

The Montebellos lie about 120 km west of Dampier, 80 nautical miles from Onslow and 120 from Exmouth. There is no day-trip access for most divers: visits are by liveaboard or charter vessel (Montebello Island Safaris, based in Exmouth, runs multi-day charters and advertises dive liveaboards) or by private ocean-going boat, typically a 6–10 hour passage, anchoring in the islands' sheltered lagoons. Carry full safety and communications gear; there are no facilities.

Diving is best April–October outside cyclone season. The islands have a large tidal range (about 6 m at springs), driving strong currents through the channels; dive at slack water. Visibility is unpredictable — one operator suspended charters in 2022 partly because visibility often struggled to exceed 5 m — while the western outer reefs can be much clearer on calm days.

South-westerly and easterly winds limit which anchorages are usable.

From a private vessel, dive the fringing reef slope at 5–12 m on slack water, staying in the water (no landing).

No regular operator – private vessels only.