The Arch is one of the signature boat dives at Bass Point, a short run from Shellharbour Marina past the mouth of Bushrangers Bay. The arch sits on a ridge that runs at right angles to the shoreline, extending seaward just beyond Bass Point Island. It is roughly 20 m long, 10 m wide and three to five metres high with a sand floor at about 26 m, so it is more a short tunnel through the ridge than a delicate bridge, and it is wide enough for a group to swim through comfortably.

West of the arch, at about 18 m, is a sizeable cave with two chambers, and a huge bull ray is often found resting at its entrance. Through winter the site is known for Port Jackson sharks, which gather on the sand and in the crevices of the ridge during their breeding season. The ridge itself carries sponges and encrusting life, with schooling bullseyes, yellowtail, leatherjackets and seapike around the rocks, and divers occasionally report the blue-kneed sea spider in the area.

The depth profile – 26 m on the sand, 18 m at the cave, shallower on the ridge – suits Advanced divers and makes a tidy multilevel dive. Although it can be reached from shore, the kilometre-plus walk and scramble over rocks, and the need for millpond conditions to enter and exit safely, mean almost everyone does it from a boat. Shallow reefs to the north and west of the point require care on approach, and in deteriorating conditions divers have the option of exiting eastward into the shelter of Bushrangers Bay.

Launch from the Shellharbour Marina boat ramp (Shellharbour Village; trailer parking and toilets), about 105 km and 1.5 hours south of central Sydney. Head east out of the harbour and around Bass Point; run about 150 m past the entrance to Bushrangers Bay towards Bass Point Island and anchor on 34° 35.978' S 150° 54.120' E (about 4 km, 10 minutes from the ramp). Shore access is possible but involves parking in Bass Point Reserve, walking over a kilometre and scrambling across rocks to the entry – only practical in millpond seas.

Bass Point juts well out to sea south of Shellharbour, so its outer reefs take swell from the north-east through to the south. Boat dives here want a swell under about 1.5 m and moderate winds; in a south-easterly the outer sites become rough very quickly, and the short run from Shellharbour Marina means operators can come back in if conditions build. Westerly winds in late autumn and winter give the best flat seas and clearest water, often 15–20 m.

Visibility drops after big seas stir the sand and after heavy rain. Shallow reefs extend north and west from the point, so approach carefully; if the surface builds while you are down, divers can exit east towards Bushrangers Bay.

Descend to the sand at about 26 m, swim through the arch, then explore the ridge it sits on. Visit the two-chamber cave on the western side at about 18 m, where a large bull ray often sits, and return to the anchor along the ridge.

Shellharbour Scuba and Photography Centre runs boat dives around Bass Point from Shellharbour Marina when numbers allow; United Divers (Fairy Meadow) and Sydney-based operators such as Expedition Dive run occasional charters; most other visits are private and club boats.