Aughinish Rock is an isolated shallow reef about 3 km south of Montague Island. The Marine Life Network describes a large shallow plateau whose outer edges drop to 20–30 m, packed with sponges and soft corals. It is best known as the reef that sank the SS Lady Darling. Just after midnight on 10–11 November 1880, the Lady Darling's chief officer changed course and the ship struck Aughinish Rock on her port side near the engine room; she sank some 5.5 km to the south-west.

The plateau is shallow enough to break in large swell and is covered in kelp and encrusting algae, with blue groper, wrasse, sweep and schools of yellowtail and silver trevally. The outer walls are the highlight: sponges, soft corals, gorgonians and sea squirts in many colours, with bullseyes and eastern blue devilfish in the crevices. Being isolated and exposed, it attracts pelagic fish, and seals from Montague often pass through.

The dive suits Advanced divers who can manage a wall to 30 m and possible current, though Open Water divers can enjoy the plateau with a guide. It combines naturally with a dive on the Lady Darling. Coordinates here are estimated from the descriptions (3 km south of Montague and 5.5 km north-east of the wreck) and should be confirmed. McFadyen spells the name Anghinish. Because it is exposed and some distance from Narooma, it is dived far less often than the island sites, and a calm, clear day here is something of a prize for local divers. Operators usually decide on the morning whether conditions justify the longer run.

Boat access only. Narooma Charters leaves from the Narooma town wharf on Wagonga Inlet (about 25 minutes to the island) and Underwater Safaris from Narooma marina; private boats launch at the Apex Park or Bar Beach ramps inside the inlet. Every trip crosses the Narooma bar, one of the most dangerous on the NSW coast, so departures depend on bar conditions; Bermagui harbour (about 24 km by sea) is the fallback launch point.

Aughinish Rock is about 3 km south of the island (MLN) and roughly 5.5 km north-east of the Lady Darling wreck (McFadyen), so it is a longer run than the island sites and is often combined with the wreck. Bermagui boats can also reach it.

Montague Island is about 9 km offshore and fully exposed, but with sites on all sides operators can usually find shelter from the wind of the day: the northern bays in southerlies, the western side in easterlies. The real limit is the Narooma bar, which closes in moderate easterly or southerly swell, especially on a run-out tide; McFadyen calls it probably the most dangerous bar in NSW. Trips are frequently delayed or cancelled, so allow spare days.

Currents are strong on the northern and eastern sides. Aughinish Rock is fully exposed with no island shelter, and its shallow plateau breaks in big swell. It needs a calm day with little current.

Descend onto the plateau at 5–10 m, then go to the outer edge and drop down the wall to 20–30 m through the sponges and soft corals. Work along the edge, then come back up onto the plateau for the rest of the dive.

Dived occasionally by Narooma operators and Sydney club trips in good weather; listed by the Marine Life Network and McFadyen.