The Arch is a small natural archway near the northern side of Split Solitary Island, close to the dramatic cleft in the rock that gives the island its name and which is visible from the surface as the island's most distinctive feature. Underwater, the archway itself is modest in scale compared with the more famous Manta Arch at South Solitary Island, but it offers a brief, scenic swim-through well within Open Water depth limits, in a comfortable 8 to 16 m range typical of this closest and most sheltered island in the group. Because Split Solitary Island is the default fallback site whenever weather rules out the more exposed islands further offshore, The Arch sees fairly regular use as part of a broader dive plan, usually worked in en route between the northern approach and one of the island's several named southern moorings such as Turtle Cove or Cod Rock.

Moray eels are commonly found in the archway's crevices, nudibranchs and other invertebrates decorate its walls, and turtles and reef fish pass through the opening regularly, making it a worthwhile few minutes on any Split Solitary Island dive rather than a stand-alone destination. Given Split Solitary Island's popularity as the marine park's most heavily used training and fallback site, The Arch benefits from being genuinely low-risk and straightforward to navigate, suiting divers at every experience level from open-water students to instructors looking for a reliable, attractive feature to include on an otherwise flexible dive plan. It is not marketed with the fanfare of South Solitary Island's headline sites, but as a small bonus feature within an already excellent, reliable dive location, it adds real value to a Split Solitary Island visit.

Jetty Dive Centre departs from the public floating pontoon wharf in Coffs Harbour boat harbour; Split Solitary Island is about 20 minutes out, the closest of the group.

Split Solitary Island, being the closest and most sheltered of the group, is the most consistently diveable island; visibility is often lower than at South Solitary Island since it sits closer to the mainland's influence.

Approach the archway from open water at 10-12 m, pass through slowly checking the walls for moray eels and nudibranchs, and continue on to one of the island's named southern moorings to complete the dive.

Jetty Dive Centre includes The Arch as part of a broader Split Solitary Island dive when the mooring plan allows a pass by the island's namesake split.