Sterile Island is a small, barren rock in the Actaeon Reef chain at the southern entrance to the D'Entrecasteaux Channel. The Marine Life Network guide describes bull kelp on its seaward side and a reef that runs just below the surface for many kilometres, in 5-9 m, and notes that the wooden ship Wallace (338 tons) was wrecked here in 1835, with cannon and ironwork remaining. It requires exceptionally calm weather.

The shallow reef is dominated by bull kelp and brown algae, with abalone, sea urchins, wrasse, leatherjackets and magpie morwong. The Wallace remains give the site its particular appeal: cannon and ironwork concreted into the reef are a tangible link to the early colonial shipping that used the Channel as its gateway to Hobart – and to the dangers of the reef, which also claimed the Actaeon in 1822. All material is protected historic heritage; it must not be disturbed or removed, and sightings of artefacts can be reported to Heritage Tasmania.

The site is extremely exposed and only reachable on rare calm days, and the shallow reef poses a real navigation hazard for boats. It is best combined with Actaeon Island's more sheltered kelp forest on the same expedition day. The far south has no dive shop or air fills – bring filled cylinders from Hobart or Kingston – and mobile coverage is patchy, so carry a VHF radio and leave a trip plan.

Allow plenty of margin for the run home, as weather at the Channel entrance can change within an hour.

Recherche Bay is at the end of the Huon Highway and the gravel road beyond Southport and Lune River, about 2 hours (110 km) south of Hobart; it is Australia's southernmost road-accessible coastline. The Catamaran River boat ramp at the southern end of the bay is the usual launch; Cockle Creek has camping and is the start of the South Coast Track. Sterile Island is part of the Actaeon Reef chain; access is by boat from Recherche Bay or Southport in exceptionally calm weather, about 30 minutes.

The reef extends just below the surface for many kilometres – navigate with great care and local knowledge.

The far south – Port Esperance, Southport and Recherche Bay – opens southward to the Southern Ocean. Southerly and south-westerly swell and strong southerly winds make the exposed sites unworkable and quickly reduce visibility, while northerly and light westerly winds give calm water. Sheltered bays such as Port Esperance and inner Recherche Bay remain diveable in moderate conditions.

Weather changes rapidly and fronts arrive every few days; plan around high-pressure systems in late summer and autumn and watch for south-westerly changes. The Marine Life Network stresses that exceptionally calm weather is needed at Sterile Island.

In flat calm only, anchor in the lee, explore the shallow reef at 5-9 m looking for the cannon and ironwork of the Wallace, and avoid the bull kelp zone on the seaward side if any swell is present.

No regular operator; private expedition boats only.