Dunk Island, Coonanglebah to its Traditional Owners, is the largest of the Family Islands, a rainforest-covered continental island about 4 km off Mission Beach that is mostly national park. It was long known for its resort, which was wrecked by Cyclone Yasi in 2011, and today visitors come by water taxi for the day or to camp at Brammo Bay. Fringing reefs surround parts of the island, and its beaches, Brammo Bay, Muggy Muggy, Pallon and Coconut, provide access to corals, reef fish, sea turtles and occasionally dugongs.

It is primarily a snorkelling destination rather than a scuba site. The reefs are shallow inshore fringing reefs, and because the island is close to the mainland and near the Tully and Johnstone river outflows, visibility is usually modest, often 3-10 m and worse after rain. The coral is typical of inshore reefs, with robust hard corals, soft corals tolerant of turbid water, and mixed fish including parrotfish, damsels, butterflyfish and rabbitfish, and turtles feeding over seagrass and reef.

Local tour operators take visitors by boat to the best coral spots around the island, and some divers do shallow shore dives from the beaches, but there is no dive shop on the island and scuba gear must be brought across. The island's appeal lies in combining a snorkel with rainforest walks, birdlife and beaches, and in the non-stinger season from May to October the water is pleasant without a stinger suit. Serious divers should head to the outer reefs, 60-90 minutes further out.

Dunk Island is about 4 km off Mission Beach. Water taxis and ferries run from Wongaling Beach and from the Clump Point jetty (about 10-20 minutes), landing on the beach or jetty at Brammo Bay, where the day-use area and camping ground are. Mission Beach is 1 hour 45 minutes' drive south of Cairns; park near the departure beach.

From Brammo Bay, Muggy Muggy Beach is a walk of about 1.5 km along the island track. Carrying scuba gear on the island is impractical for most, so the fringing reef is mainly snorkelled from the beaches, or dived from a local tour boat that visits the best coral spots around the island.

The Mission Beach reefs are exposed to the south-east trade winds, which blow 15-25 knots for much of April-September and can cancel trips; the calmest months are usually September-December. Box jellyfish and Irukandji are present from about October-November to May, most dangerously close to the coast, so wear a full stinger suit. The cyclone season runs November-April, and Mission Beach has been hit hard by cyclones Larry (2006) and Yasi (2011).

Heavy wet-season rain and river flood plumes from the Tully and Johnstone rivers reduce visibility on the inner reefs. Dunk is close to the mainland, so visibility is usually only 3-10 m and poor after rain; the north-western beaches are sheltered in south-easterlies. The non-stinger season (roughly May-October) is the comfortable time to swim without a suit.

Snorkel or dive from the beach at mid to high tide: swim out over sand to the fringing coral at 2-5 m and follow the reef edge parallel to the shore, turning at half gas or when the reef ends, and return the same way.

Dunk Island water taxis and ferries from Mission Beach (daily); local snorkel and reef-tour boats visit coral spots around the island; no dedicated dive shop on the island