Cape Willoughby is the eastern tip of Kangaroo Island, where South Australia's first lighthouse was lit in 1852 to guide ships through Backstairs Passage.

The cape faces the open junction of Backstairs Passage and the Southern Ocean. Tidal streams run hard around the point, and swell from the south and south-east breaks on the rock platforms. Underwater, divers can expect granite and limestone reef with kelp and brown algae, ledges and boulders sheltering rock lobster, and the fish of current-swept headlands – sweep, salmon, trevally, kingfish and western blue groper. Sea lions and fur seals range along this coast, and the same currents that bring fish also bring larger predators.

Nearby Antechamber Bay, to the north-west, is more sheltered and holds the remains of the schooner Kona, and Penneshaw offers easier shore diving. The Cape Willoughby lighthouse is open for tours, with cottages available to stay in. For experienced divers with a boat, calm weather and good knowledge of the tides, the cape could offer lively, fishy reef diving; for others it is a place to visit on land. Visiting divers who want to try it should seek local knowledge first – the island's fishers and the Kingscote dive shop know the tides and landing spots. Carry a DSMB and signalling device, and brief a shore contact on your plan before entering the water.

Take the SeaLink ferry from Cape Jervis to Penneshaw (45 min). From Penneshaw drive about 28 km south-east on Willoughby Road (partly unsealed) to the Cape Willoughby Conservation Park and lighthouse. Park at the lighthouse car park.

Shore entries are over steep rock platforms exposed to swell and current; a boat from Penneshaw or Antechamber Bay is the safer option in calm weather.

The Dudley Peninsula sites lie on Backstairs Passage and Eastern Cove, sheltered from the prevailing south-westerly swell but swept by strong tidal streams through the passage. Dive around slack water, particularly near headlands and islands; wind against tide creates steep chop. Easterly and north-easterly winds make Penneshaw and Hog Bay choppy, while south-easterlies affect Antechamber Bay and Cape Willoughby.

Summer and autumn bring the calmest days; winter westerlies are usually fine on this side of the island. Cape Willoughby itself is exposed to south-easterly and southerly swell and to the full tidal flow around the cape; dive only at slack water in calm weather.

At slack water, enter from a sheltered gutter or anchor in the lee, explore the kelp-covered ledges at 6-15 m, and exit or ascend on a DSMB before the tide turns.

No regular operator – private boats and experienced shore divers.