Gull Rock is a small rocky islet at the southern end of Maslin Beach, where the orange and white cliffs give way to the Aldinga coast. The Scuba Divers Federation lists it among the metro shore dives, noting that the reef extends out from the rock for several hundred metres, from just below the surface to about 10 m, and can be reached by boat from O'Sullivan Beach or from the beach. Detailed descriptions of the underwater topography are limited.

The reef is part of the same limestone system that runs south into the Aldinga Reef Sanctuary Zone, and it can be expected to show low ledges, holes and boulders carpeted with brown algae and kelp in the shallows, with sponges and ascidians in shaded spots. Fish such as old wives, magpie perch, zebrafish, sweep, leatherjackets, wrasse and blue devils are typical of this coast, and cuttlefish and nudibranchs are likely. The attraction is a quiet, shallow reef that few people dive, in a scenic setting.

It suits Open Water divers and snorkellers on flat days, and boat divers heading to Aldinga who want a shallower alternative. Shore divers should be aware that the southern end of Maslin Beach is an official unclothed beach, and that the carry from the car park involves a path down the cliff and a walk along the sand. As with other less-documented sites, divers are encouraged to report observations to the Federation.

Keep an eye on the weather: the site is only worth the walk in calm conditions.

By boat, launch at O'Sullivan Beach ramp and run south about 15-20 minutes past Port Noarlunga and Moana to the southern end of Maslin Beach. By land, drive to Maslin Beach (about 45 minutes south of Adelaide via Main South Road) and park at the southern Maslin Beach car park at the end of Tait Road; walk down the path and along the beach to the rock and enter from the sand. Note that the southern end of Maslin Beach is a designated unclothed (nudist) beach.

SDFSA also mentions beach access south of Aldinga Reef.

Maslin Beach faces west into the gulf, so Gull Rock needs calm seas after offshore easterly winds. Westerly and south-westerly swell produces surf on the beach and surge around the rock, and the summer sea breeze usually builds by early afternoon. Tidal flow is mild.

Visibility is generally better than further north because there is less river influence, but drops after strong winds.

From the rock, follow the reef seaward at 3-8 m keeping it on one shoulder, turn at half gas and return along the other side to the rock.

No regular operator; listed by SDFSA and occasionally dived by clubs and private boats from O'Sullivan Beach.