Wedge Island is the largest of the Gambier Islands, a remote group at the mouth of Spencer Gulf south-west of Yorke Peninsula. Low in the north and rising to about 200 m in the south, it has spectacular 150 m cliffs on its north-east side. The SDFSA describes lots of walls, drifts, swim-throughs and caves to 50 m with prolific fish life, and it is widely regarded as one of the wildest and least-dived sites in South Australian waters.

The best-documented site is Shark Cove, a 100 m indentation in the cliffs described by the Marine Life Society: a narrow ledge about 6 m wide surrounds two-thirds of the cove, with long undercuts and vertical walls dropping to seagrass and kelp-covered boulders at around 25 m. The walls carry yellow zoanthids, soft corals, gorgonians and sponges, and old wives, blue devils, blue groper and leafy seadragons are recorded. In the northern part of the cove a small cavern leads to a wide tunnel penetrating North Point and opening to the sea, with an air pocket at 3 m large enough for a diver's head – the air is presumed stale, so regulators should stay in.

Seals visit often, though fish life at Shark Cove itself is described as relatively modest. Other sites around the island offer sheer walls, deep ledges and drift dives in clear oceanic water, and West Bay (listed separately) has boulder-covered crevices and rich invertebrate life. Wedge Island is an expedition dive: a long, exposed crossing, strong currents, great depths and no help nearby.

It suits highly experienced divers with a large boat and patience to wait for the right weather.

From Adelaide drive about 300 km (3.5 hours) via Port Wakefield, Minlaton and Warooka to Marion Bay; Dhilba Guuranda-Innes National Park begins just west of the township (vehicle entry fee, pay online or at the Stenhouse Bay visitor centre). Launch at the Pondalowie Bay ramp inside the park (west coast of Innes) and run about 25-30 km west across open water to Wedge Island – 1 to 1.5 hours depending on boat and sea. This is a serious open-ocean crossing: the Marine Life Society advises picking your day and having a big boat.

The island is privately leased; do not land without permission.

The southern tip of Yorke Peninsula faces the open Southern Ocean and Investigator Strait, so south-westerly and southerly swell is the controlling factor: most exposed sites need swell under about 1.5 m and are best after several days of northerly or north-easterly winds, which blow offshore along this coast. Winter cold fronts bring big south-westerly swell and strong winds and can close the area for days. Summer afternoon south-easterly sea breezes make boat runs rough, so launch early.

Visibility is typically 10-20 m in settled conditions but drops sharply with swell-driven surge. Wedge Island lies in open ocean with strong tidal and oceanic currents; it needs a multi-day window of light winds and low swell to make the crossing safely.

At Shark Cove, descend beside the 6 m ledge and follow the undercuts and vertical walls around the cove, checking the small cavern and tunnel through North Point (do not remove regulators in the air pocket). On other sites, drift along the walls with a surface tender following SMBs.

Depth to 50 m available – technical training and appropriate gases for anything beyond 40 m; conservative profiles given the distance to the chamber.

No commercial operator; visited only by occasional private expeditions and club trips with large boats from Pondalowie Bay or Port Lincoln-based vessels.