Mistaken Cape, the easternmost point of Maria Island, is rated 9.5 out of 10 by the Marine Life Network guide, which calls it a real expedition-style dive. The site is a reef about 200 m wide with rock spires in 20-40 m of water and stunning visibility, reached only after a long boat trip from Dunalley or Orford via Darlington.

The guide describes yellow zoanthids covering rock faces up to 15 m high, sea whips, basket stars, hydroids and abalone, with leatherjackets, wrasse and clouds of butterfly perch. That profile - deep granite spires plastered with zoanthids and whips in clear oceanic water - is similar to the best Governor Island sites at Bicheno, but in a far more remote and rarely visited setting.

Maria Island is a national park with no permanent residents apart from rangers, and the Darlington settlement preserves convict-era buildings from 1825 onwards. The marine reserve along the island's northern and western shores has been no-take since 1991 and has been used for long-term studies of how protection affects rock lobster and fish numbers, so reef life inside it is noticeably richer than outside.

Maria Island's boat sites are rarely visited because there is no operator on the island and the eastern coast is a long way from the Triabunna ramp. Visitors with their own boats should carry oxygen and a radio, check the forecast for Mercury Passage as well as the open coast, and remember that the Royal Hobart Hospital chamber is roughly two hours away by road once back at Triabunna.

Triabunna, on the Tasman Highway 1 hr 15 min (85 km) north-east of Hobart, is the gateway. The Maria Island passenger ferry (Encounter Maria Island) runs several times daily from Triabunna to the Darlington jetty, about 16 km and roughly 30-45 minutes; it carries people and small amounts of luggage but not vehicles, and dive cylinders should be cleared with the operator first. Private boats launch at the Triabunna ramp (best), Saltworks Road ramp, or Orford (shallow bar at the Prosser River mouth - difficult at low tide).

Mistaken Cape is on the exposed eastern coast; the Marine Life Network guide describes it as a long boat trip from Dunalley or Orford, usually via Darlington and around the north of the island - allow 1-1.5 hours from Triabunna.

Maria Island's western and northern shores (Darlington, Fossil Cliffs, Painted Cliffs) are sheltered from easterly ocean swell but exposed to strong westerlies and north-westerlies blowing across Mercury Passage, which are common in winter and spring. The eastern side (Mistaken Cape, Bunker Bay) faces the open Tasman Sea and needs westerly weather and small swell. Southerly swell wraps around Cape Peron and the southern end.

Visibility drops after rain as runoff flows from the Prosser River into Mercury Passage. Mistaken Cape needs westerly weather and swell under about 1 m; any easterly swell makes it undiveable.

Descend onto the reef at 20-25 m and explore the rock spires, staying within no-decompression limits unless trained for decompression. Ascend along a spire to finish with a long safety stop. 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.

Nitrox or trimix and decompression planning appropriate for the deeper spires.

No operator based on Maria Island. Hobart shops run occasional trips: Go Dive Tasmania has offered Ile des Phoques seal dives and filmed Troy D dives; Tasmanian Scuba Diving Club and Tas Uni Dive Club run club trips from Triabunna. Most diving is from private boats.