Fossil Bay lies between Darlington and the Fossil Cliffs on the northern coast of Maria Island. The Marine Life Network guide rates it 6 out of 10 and describes two options: the Fossil Cliffs end, with a quick drop to 8-10 m, and the north-eastern end, at 5-8 m along the cliffs. Leatherjackets, wrasse, sea sweep, trumpeter and butterfly perch are the common fish.

The guide notes that, paradoxically, the bay was a marine reserve but open to fishing when it was written. The current Maria Island Marine Reserve rules prohibit all fishing and collecting within the reserve boundary, which runs along this coast, so check the latest boundary before assuming either way.

Fossil Bay is an easy dive suitable for new divers and a good alternative to the deeper Fossil Cliffs swim-through next door. The limestone reef contains fossils like the cliffs above it, and the bay is also a good snorkel on calm days.

Access is by boat from Triabunna or by kayak from Darlington. There is no dive operator on the island, so bring filled cylinders and all equipment, and plan the day around the ferry timetable if staying at Darlington.

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.

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).

Fossil Bay is just east of Darlington, around 30-35 minutes by boat from Triabunna. It is a short boat ride from the Darlington anchorage.

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. Fossil Bay is sheltered from southerly and easterly weather and is usually calm in the morning.

Choose either end: at the Fossil Cliffs end drop in at 8-10 m where the bottom falls away quickly; at the north-eastern end follow the cliffs at 5-8 m. Return along the same route. 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 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.