Fourth Sister is an underwater extension of the Three Sisters islets near Ulverstone - about 300 m long and 70 m wide on average - that terminates in a pinnacle rising to within 3 m of the surface. The Marine Life Network guide rates it 6 out of 10: 10-18 m, with a slight current that enhances filter-feeding animals and fish schools. Bastard trumpeter, sea sweep, long-finned pike, large schools of barber perch, southern hulafish, leatherjackets and wrasse are recorded, along with gorgonian fans, many of which appeared dead, and the guide notes pollution and siltation concerns. The Leven Scuba Club describes a 300 m reef ending in a pinnacle, affected by current and visited by pelagics. Local knowledge from Leven Scuba Club members is the best way to get the most out of it, and first-time visitors should ideally dive it with someone who knows the site and the tide.

The central north coast between Wynyard and Port Sorell is the home water of the Leven Scuba Club at Ulverstone, whose site list is the main modern source for it, supplemented by the older Marine Life Network guide. The towns of Burnie, Ulverstone and Devonport sit right on the coast, so many sites are within minutes of a ramp or car park, but the reefs are generally low and weedy, visibility is often 5-10 m, and the coast is open to Bass Strait's northerly and westerly weather.

Devonport is the Spirit of Tasmania ferry terminal, which makes these sites the first and last dives for many interstate visitors bringing their own gear. There is no hyperbaric chamber in the north - the nearest is the Royal Hobart Hospital, about 3.5 hours' drive - so dive conservatively, especially on the deeper offshore sites.

Ulverstone is on the Bass Highway 20 minutes west of Devonport. Launch at the Ulverstone (Leven River) ramp and run west 10-15 minutes to the Three Sisters islets off Goat Island; enter near the jagged foreshore rocks at the north-western tip of the Third Sister and follow the reef out. From the Spirit of Tasmania terminal at Devonport, all central north-coast sites are within about an hour's drive along the Bass Highway.

North-coast ramps are often shallow and weedy at low tide, so time launches for mid to high tide and carry a sounder, radio and tide tables.

The north-west coast faces Bass Strait: north-westerly to north-easterly winds and westerly swell make it rough, while southerly winds blow offshore and give flat seas - light airs and sunny days are relatively common from January to April. Easterly gales are common in the warmer months and close the eastern faces of Rocky Cape and Sisters Island. Tidal streams run along the coast (eastward on the flood), and several boat sites are only comfortable around slack water.

Affected by current, which brings in pelagics and feeds filter feeders.

Drop at the Third Sister and follow the 300 m reef (about 70 m wide) out to the pinnacle, diving at 10-18 m, then ascend on the pinnacle. Turn the dive at half gas (thirds where current or overhead sections are involved), deploy an SMB before surfacing for the live-boat pick-up, and complete a 3-minute safety stop at about 5 m where depth allows.

No confirmed commercial dive operator on the north-west coast as of 2026 (older guides mention dive services in Wynyard and Devonport - verify). Sites are dived mainly by the Leven Scuba Club (Ulverstone), other north-west club members and visiting divers with their own boats; Tasmanian Divers (Launceston) runs occasional northern trips.