The Neptune Islands are the centre of Australian white shark tourism and one of a handful of places in the world where great whites can be reliably seen from a cage. Named by Matthew Flinders in 1802, the two groups – North Neptune and the South Neptunes – are rocky granite islands about 40 nautical miles south of Port Lincoln. They support Australia's largest colony of long-nosed (New Zealand) fur seals, around half the national breeding population, plus Australian sea lions, and it is the seals that draw the sharks.

The waters are protected as the Neptune Islands Group (Ron and Valerie Taylor) Marine Park, named for the pioneering underwater filmmakers who shot shark footage here. Port Lincoln's association with white sharks goes back to Rodney Fox, who survived a near-fatal attack in 1963 and went on to design the first shark-viewing cage; footage filmed in these waters contributed to Jaws. Today the South Australian White Shark Tour Licensing Policy limits cage diving to two licensed, eco-certified operators and regulates how they attract sharks, and the Department for Environment and Water publishes annual reports on shark visitation.

The experience is straightforward. The boat anchors in the lee of an island, a cage is lowered alongside, and small groups take turns in the water breathing from regulators fed from the surface or snorkelling. Sharks – males of up to about 5 m year-round, and females up to 6 m mainly in winter when seal pups take to the water – circle the boat and pass within arm's reach of the bars.

No dive certification is needed for the surface cage. Rodney Fox's liveaboard adds an ocean-floor cage for certified divers, lowered to the seabed at around 20 m, and island walks on North Neptune. Bronze whalers, dolphins, seals and occasionally mako sharks and whales are also seen.

Sightings are never guaranteed – some trips see several sharks, others none – and the crossing can be rough. For anyone who can handle a long boat day, it is one of the world's great wildlife encounters.

Port Lincoln is about 650 km (7 hours) by road from Adelaide via Port Augusta and the Lincoln Highway, or a 45-50 minute flight (Rex/QantasLink). All trips depart from Port Lincoln's Lincoln Cove Marina. Calypso Star Charters runs one-day trips (typically a 6-7am departure, 2.5-3 hours each way, returning in the evening).

Rodney Fox Shark Expeditions runs liveaboard expeditions aboard MV Rodney Fox of 2, 3 or 5+ nights, anchoring in protected coves at the islands. There is no independent access: diving with white sharks at the Neptunes is only permitted through licensed operators.

The Neptune Islands sit in open ocean at the mouth of Spencer Gulf, about 70 km (40 nautical miles) south of Port Lincoln, and are very exposed and remote. Trips run year-round but are regularly cancelled or rescheduled for south-westerly swell and strong winds; day boats need a reasonable forecast for the 2.5-3 hour crossing each way, and seasickness is common. Operators hold the cages in the lee of the islands.

Winter (roughly April-August) is colder and less predictable but brings the largest females; summer and autumn offer calmer weather with regular sightings of males. Water is typically 14-20°C, and visibility varies from 5 m to more than 25 m.

Surface cage: operators rotate small groups into the cage alongside the boat in 30-45 minute sessions while sharks are attracted with berley (Calypso) or other licensed methods. Ocean-floor cage (Rodney Fox): certified divers are lowered to the sand at about 18-22 m inside the cage, watching sharks cruise past at eye level, then winched back up; bottom time is limited by depth and cold.

Ocean-floor cage dives are short, cold, deep-ish (18-22 m) bottom dives with surface support; bring or hire a drysuit in winter.

Two licensed operators under the SA White Shark Tour Licensing Policy, both advanced eco-certified: Calypso Star Charters (Port Lincoln, one-day trips several times a week; the only day operator permitted to use berley; it has also purchased Adventure Bay Charters, formerly known for acoustic/music attraction) and Rodney Fox Shark Expeditions (MV Rodney Fox liveaboard, 2-5+ nights, surface and ocean-floor cages, landing rights on North Neptune).