The Swains are the most remote reefs of the southern Great Barrier Reef: around 1,000 reefs spread across the outer shelf, separated by channels 30-80 m deep, with the continental slope dropping to about 1,000 m just offshore. Diving is by liveaboard or private yacht only, and divers must be self-sufficient, with no assistance nearby. Snake Reef is listed by the Marine Life Network as having very deep walls for the experienced diver, packed with colourful growths and visited by schools of pelagic fish, at 30-40 m.

It offers the kind of big-wall diving the Swains are known for, in clear offshore water. The walls carry sponges, gorgonians and soft corals, and the open water beside them brings trevally, mackerel and sharks. Because the best of the wall lies deep, divers should plan conservatively: the nearest hyperbaric chamber is many hours away by aeromedical evacuation.

The site suits experienced deep divers only. Most recreational divers will enjoy it within 30 m, with the upper wall still well decorated. It was grouped with Middle Cay in the earlier database pass; the two are separate sites and are now listed individually.

The Swains lie within the Great Barrier Reef Marine Park under a mix of zones, and the nine vegetated cays of Swain Reefs National Park are among Queensland's most important seabird breeding sites and significant for endangered loggerhead turtles; most are closed to landing year-round. Anchor only on sand, check the zoning map before fishing, and carry oxygen, a satellite communicator and a detailed evacuation plan, since aeromedical retrieval to Mackay and a chamber in Townsville takes many hours.

The Swain Reefs are the most remote part of the southern Great Barrier Reef, roughly 200-250 km offshore. Liveaboards depart Gladstone Marina or Rosslyn Bay Harbour (Yeppoon) in the evening and steam overnight across the 50-mile-wide Capricorn Channel, a passage of 12-15 hours in good weather; trips run 6-10 nights. Private yachts should carry detailed charts (reefs are separated by 30-80 m deep channels) and plan for no outside assistance.

Once in the Swains, liveaboards move between reefs by day and anchor in the lee of a reef or cay at night; this site is visited as part of a multi-day itinerary.

The Swains are fully exposed. South-east trade winds of 20-30 knots, common June-August, make the Capricorn Channel crossing rough and restrict diving to the lee (north-western) sides of reefs; charter operators generally shelter behind reefs at anchor in 20-25 knots. Best windows are the calm spells of September-December and March-May.

Cyclones can reach the area November-April. Tidal currents run hard through the channels between reefs, so outer-edge sites are dived as drifts near slack water; lagoon and lee sites work in most tides.

Descend the wall to a planned maximum within your certification (no more than 30 m for most recreational divers on air), follow it briefly with the current, then ascend gradually along the wall, spending most of the dive at 15-20 m and finishing with an extended safety stop under an SMB.

Depths of 30-40 m exceed Advanced Open Water limits; appropriate deep training, nitrox (with MOD awareness) or trimix for the lower wall, redundant gas and conservative profiles are advised given the distance from a chamber.

No day operator. Kanimbla Charters runs 7- and 10-day dive and fishing charters to the Swains aboard a 25 m catamaran (all tanks and weights supplied); Eastern Voyager runs 6-7 night trips from Gladstone mainly for fishing, snorkelling and spearfishing. Most diving here is from private yachts and occasional expedition charters.