Crescent Bay is a spectacular crescent of white sand below the cliffs of Mount Brown, south of Port Arthur, reached on foot by a popular walking track from Remarkable Cave. The Marine Life Network guide describes deep cliffs at 20-25 m with delicate sponges and anemones and small crayfish, reachable by boat or by the foot track. Because the cliffs plunge into relatively deep water, the reef beneath them is below much of the surge that scours the shallower parts of this exposed coast, allowing more delicate invertebrates to grow on the rock faces.

Sponges in a range of colours and forms, jewel anemones, hydroids and ascidians cover shaded surfaces, and small rock lobsters hide in the cracks. Fish life includes wrasse, leatherjackets, butterfly perch and morwong, and fur seals patrol this coast. The site is rarely dived; access is either a boat run out of Port Arthur or a long walk that few divers will attempt with cold-water kit.

It suits Advanced divers comfortable at 20-25 m with a competent boat cover. The scenery around Crescent Bay and Mount Brown is among the best on the Tasman Peninsula, with sand dunes, dolerite columns and views to Cape Pillar and Tasman Island. Nearby Remarkable Cave, a sea cave that can be viewed from a lookout, is not a dive site – waves surge through it with great force.

Treat the published details as indicative and plan on a calm day. A private boat is the realistic option; plan a second, shallower dive inside Port Arthur afterwards to break the return run and off-gas in sheltered water.

Usually by boat from the Carnarvon Bay ramp at Port Arthur, heading south out of the harbour and around to Crescent Bay, about 15 minutes. The Marine Life Network guide also notes access on foot: the Crescent Bay track starts at the Remarkable Cave car park (end of Safety Cove Road) and takes about 1.5 hours each way over dunes and bush, which makes carrying dive gear impractical for most. Boats should anchor in sand away from the cliff base or run live.

Crescent Bay faces south-east into Storm Bay and the open Tasman Sea, and receives the full force of southerly and south-easterly swell – it is a well-known surf and wild beach. Only dive after several calm days with northerly or westerly winds and swell under about 1 m. Surge at the cliff base can be significant even in moderate swell, but the 20-25 m depth helps.

Autumn is the best season.

Descend at the base of the cliffs to 20-25 m and follow the wall, looking closely at the sponge and anemone patches on shaded rock. Ascend along the cliff and deploy an SMB for pick-up clear of the rock.

No regular operator; private boats from Port Arthur and occasional club trips.