New Arch is the deeper of the two arch dives at Moon Island. Grey Nurse Charters describes a large arch spanning a narrow gutter at around 24 m, with a series of gutters to explore and colourful coral growth throughout. iNaturalist's Moon Island notes call it New Arch or Wide Arch and place it to the south among the gutter formations. The gutters are the defining feature.

Long channels cut into the reef, each with walls a few metres high, provide natural routes and shelter for fish and invertebrates. The arch itself is a slab of rock bridging one narrow gutter, making a swim-through that frames divers against the light. Its walls and ceiling carry sponges, ascidians, soft corals and encrusting growth - the colourful coral growth Grey Nurse Charters refers to - and the shade suits cryptic species such as nudibranchs, shrimps and small cardinalfish.

Fish life is abundant, with yellowtail and silver sweep over the gutters, bullseyes and pomfrets in the arch and overhangs, red morwong and blue groper along the walls, and wobbegongs resting in the gutter floors. Moon Island's wider cast - eastern blue devils, weedy seadragons, bull rays, Port Jackson sharks and, in winter, grey nurse sharks - may all turn up. At around 24 m the site needs Advanced certification or guided experience at depth.

It offers more depth and a sense of discovery than The Arch closer in, and it suits divers who enjoy navigating reef topography. Good buoyancy is important in the narrow gutters to avoid damaging the delicate growth on the walls and ceiling.

Boats launch from the public ramps inside Swansea Channel, either at Black Neds Bay beside the Swansea Bridge or at the Swansea/Lake Macquarie ramps, about 25 km south of Newcastle via the Pacific Highway. Parking with trailer bays is available at Black Neds Bay. The run is east along the channel, across the Swansea bar (check the bar and tide first - cross on the flood where possible) and a short distance out to the site; Moon Island sits just off Swansea Heads (Reids Mistake), so the run from the bar is only a few minutes - total 10-15 minutes from the ramp.

New Arch is among the gutters to the south of the island, a little further out than The Arch.

Moon Island and the reefs off Swansea Heads sit just outside the Swansea Channel bar, which is the deciding factor on most days: the bar is dangerous in any sizeable easterly or south-easterly swell and on a run-out tide, and Marine Rescue Lake Macquarie should be checked before crossing. Offshore, the sites prefer swell under about 1.5 m and light westerly or northerly winds; a strong nor'easter makes the eastern walls choppy, and a southerly swell pushes surge into the caves. Visibility runs 8-15 m and is best on a flooding tide, when clean ocean water replaces the lake outflow; after heavy rain the brown plume from Lake Macquarie can cover the inshore sites for days.

New Arch is exposed to southerly swell, which pushes surge through the gutters.

Descend to the gutter system and locate the arch spanning the narrow gutter. Pass under it if surge allows, then explore the neighbouring gutters in sequence before returning to the anchor with a safety stop.

Grey Nurse Charters (Swansea) runs boat dives to the Moon Island and Swansea offshore sites most weekends and on demand; Dive Newcastle and local clubs also dive the area from private boats launched at Swansea.