The Arch is one of Jervis Bay's best-known advanced dives, a deep gully and arch below the cliffs just north of Point Perpendicular, about 200 m offshore. The gully is roughly 7 m wide and 25 m long, dropping to about 35 m, and on its eastern side at depth an underwater arch opens out – a huge suspended rock formation shaped like an ancient stone bridge, spanning about 10 m and rising some five metres above the seafloor. The arch sits at about 37 m, and depths reach 40 m further out.

Outside the gully the terrain is boulder-strewn, with small rocks and very large boulders to the north. The southern outside wall is an excellent vertical face extending for at least 100 m. The fixed growth on the arch walls and roof is outstanding – sponges, small gorgonian sprigs and anemones – and schools of striped seapike and yellowtail hang in the gully. Several species of leatherjackets are common, wobbegongs rest on the bottom and in winter the site is famous for Port Jackson sharks, with McFadyen counting up to 60 on one dive.

Visibility is normally very good, commonly 25–30 m, which adds to the sense of scale. But at 35–40 m this is a genuine deep dive: narcosis is noticeable, no-deco time is short (20–24 minutes including the gully), and the exposed location means current can occasionally run. It suits Advanced divers with deep training and experience, ideally on nitrox or with a planned staged ascent. For those divers it is a highlight of the NSW South Coast.

Charters depart Huskisson (Dive Jervis Bay; boats in Currambene Creek). Private boats launch at Huskisson, Callala Bay or Murrays Beach (Booderee), or at Currarong's ocean ramp. From Huskisson cross the bay to the entrance and turn north around Point Perpendicular onto the outside of the Beecroft Peninsula; run north of Point Perpendicular towards the massive gully in the cliff.

Line up the front left side of the gully with its back right side and run in on the sounder: expect 40+ m, a rise to 28 m, a drop to 35 m and a final rise to 25 m. Anchor at 35° 04.989' S 150° 49.270' E (about 25–30 minutes from Huskisson).

The outer Beecroft Peninsula cliffs face east to south-east and take the full force of any south-easterly or easterly swell; the sites are diveable in swell under about 1.5 m and are well sheltered from south-westerly and westerly winds, which make them the go-to sites in winter. North-easterly winds (common on summer afternoons) make the run from Huskisson across the bay entrance rough and cause surge on the northern-facing cliffs. Visibility is commonly 15–25 m and can reach 30 m in winter when clear oceanic water sits against the peninsula.

Currents along the cliffs are usually mild but can run at the bay entrance on a strong tide change. Defence live-firing closures can shut the sea area – check before going.

Descend the anchor line into the gully (about 7 m wide, 25 m long, 35 m deep), explore the arch opening on its eastern side at about 37 m, then follow the outside northward to the very large boulders. Return through the gully, look under the arch's southern wall and, air permitting, follow the south exterior wall. Budget 20–24 minutes bottom time and a staged ascent.

EAN28 suits the 35–37 m profile (check MOD); plan a staged ascent; carry a DSMB.

Dive Jervis Bay (Huskisson; boats Avalon and Genesis) runs double boat dives most days, and Deep 6 Diving Jervis Bay / other Huskisson operators also visit; site chosen on the day according to swell and wind. Run as an advanced/deep dive for suitably qualified divers.