The Arch is the best-known of the Black Rock sites, a small island off Lilli Pilli on the southern shore of Batemans Bay. Michael McFadyen describes the dive in detail: from an anchor on rocky bottom in about 10 m on the western side of the southern end of Black Rock, divers drop to the sea floor, reach a wall and follow it south past a small gutter. After crossing a section blocked by large boulders and climbing over a ridge, you arrive in a huge bowl or amphitheatre at about 15 m. The arch itself sits at around 13 m. It is quite long – almost 10 m thick at its widest – but very low. A cave extends beneath it and other caves run under Black Rock to the north and east. The maximum depth is 19–20 m off the wall.

The Marine Life Network describes a large bowl-shaped depression with an open quasi-cave about 10 m wide, decorated with yellow zoanthids, sponges and gorgonians. McFadyen notes cuttlefish and friendly blue groper, and eastern blue devilfish under the overhangs. Wobbegongs lie in the low cave areas and Port Jackson sharks are common in winter.

The Arch is sheltered and close to the ramps, so it is one of the most reliable dives in Batemans Bay and a favourite of the local operators. The swim-throughs and caves need good buoyancy, because the fine sediment silts up easily, and a torch is worth carrying. It suits Open Water divers with a guide and is a good introduction to the more complex dives around Black Rock, such as the Bubble Cave, The Tunnel and The Chimney, which can be combined as a drift.

Boat access only. Black Rock lies just off Lilli Pilli on the southern shore of Batemans Bay; the nearest ramp is at Mosquito Bay (Lilli Pilli), a couple of minutes' run, and Beneath the Bay brings divers from the Hanging Rock ramp in Batemans Bay in about 15 minutes. McFadyen's anchor mark is on the western side of the southern end of Black Rock, on rocky bottom in about 10 m.

From there divers swim to the wall and follow it south to the amphitheatre.

Black Rock is inside the southern arm of Batemans Bay and is sheltered from southerly swell, which makes it one of the most reliable sites in the bay. Strong easterly and north-easterly swell rolls in and surges through the arch and cave. Best on westerly or southerly days.

Visibility is normally good but falls after heavy rain when the Clyde River floods the bay. The caves silt up easily.

From the anchor in 10 m swim to the wall and follow it south past a small gutter, over a boulder-blocked section and a ridge into the amphitheatre at 15 m. The arch is on the far side at about 13 m; pass under it, then explore the low cave that runs back under Black Rock. Return north along the wall at 10–12 m.

Beneath the Bay dives Black Rock regularly (The Arch with swim-throughs to about 20 m, the Bubble Cave and valleys). Spirit Divers listed it as a standard boat dive; visiting Sydney clubs also use it.