Manta Arch, off the north-eastern point of South Solitary Island, is the single dive most associated with the Solitary Islands Marine Park and one of the reasons Coffs Harbour is regarded as one of the best shore-based grey nurse shark destinations on the Australian east coast. The site is built around a genuine underwater arch threading through a field of boulders and ridges, with the shallowest rock at about 15 m and gutters trailing away to a sand bottom near 30 m; the main mooring sits at 21 m directly above a boulder pile that forms the arch's entrance. From June through November this arch and its surrounding gutters host one of the most reliable grey nurse shark aggregations south of the Great Barrier Reef, with reports of anywhere from a handful up to 30, and in exceptional years 60 or more, sharks holding station in the current at once — a scene that has made Manta Arch a pilgrimage site for shark photographers from across Australia and overseas.

The sharks are almost entirely unconcerned by divers who approach slowly and keep low, and the site's name itself points to its other headline attraction: reef manta rays that pass over the boulders regularly enough, particularly in the warmer months, to have given the arch its name well before the grey nurse aggregation became as well documented as it is today. Outside the two marquee species, Manta Arch supports a dense general reef community typical of this overlap zone between tropical and temperate water: anemones and their resident clownfish colonise the boulder tops, large schools of pelagic fish move through on the current, and black cod, kingfish and assorted tropical vagrants round out a site list that changes noticeably with the season. The current here can run genuinely hard on the exposed faces, which is the main reason the site is reserved for Advanced Open Water divers and above, and why Jetty Dive Centre will switch the day's plan to the more sheltered Split Solitary Island when conditions on the north-eastern side of South Solitary Island turn unworkable.

For anyone visiting the NSW Mid North Coast with an interest in sharks, Manta Arch is the dive to build a trip around.

Jetty Dive Centre departs from a public floating pontoon wharf on the Coffs Harbour boat harbour, opposite the Attitude Burgers building — check in first at 398 Harbour Drive, Coffs Harbour. It is roughly a 30-40 minute run out to South Solitary Island, 8 km offshore, in the dive centre's RIBs. Private boats launch at the Coffs Harbour public boat ramp inside the breakwall and follow the same course out past the harbour entrance.

South Solitary Island sits in open water 8 km off Coffs Harbour and is exposed to swell from the north-east through south-east; Jetty Dive Centre generally wants under about 1.5-2 m swell to run the outer moorings comfortably, switching to the more sheltered Split Solitary Island (only 20 minutes out) on rougher days. Visibility here is usually the best in the marine park given the distance from any river mouth, and the site's position at the boundary of tropical and temperate water means conditions can change quickly with wind shift. Summer (Nov-Apr) water is warmed by the East Australian Current to up to 26°C, bringing tropical fish, manta rays and, from December, leopard sharks; winter (May-Oct) cools to about 18°C but often gives calmer seas, giant cuttlefish and the peak grey nurse shark season (Jun-Nov, sometimes 30-60+ sharks on Manta Arch).

Humpback whales migrate past between April and November, peaking June-August northbound and September-November southbound. Currents can run strongly on the exposed north-eastern moorings (Manta Arch, Shark Gutters) and are much gentler on the sheltered north-western wall.

Descend the mooring line to the 21 m boulder pile, move slowly and low across the boulders into the arch itself where sharks tend to congregate, avoid crowding the gutter entrances, and work along the ridge system to about 15 m for the return leg and ascent, using the mooring line for the safety stop given the current.

Jetty Dive Centre (Coffs Harbour) runs South Solitary Island most days conditions allow, typically a double boat dive; it is the flagship site for the only major dive operator based in Coffs Harbour.