Hallett Cove is best known on land for its geology: the Hallett Cove Conservation Park protects glacial pavements and sediments from the Permian ice age that are of international significance. Underwater, the Scuba Divers Federation lists the cove among Adelaide's metro shore dives, and Wikivoyage describes the dive as the reefy area immediately adjoining the north point of the cove, with a maximum depth of about 8 m, accessible from shore or by boat. Detailed published descriptions of the underwater topography are scarce.

The coast here is made of the same folded ancient rocks seen in the cliffs, which break into boulders, ledges and gutters at the waterline and extend as low reef out onto sand and seagrass. Expect brown algae and kelp on the shallower rock, sponges and ascidians in shaded crevices, and typical Gulf St Vincent reef fish such as old wives, magpie perch, zebrafish, wrasse, leatherjackets and blue devils. Nudibranchs and crabs are likely in the cracks.

The attraction of Hallett Cove is convenience: it is a free, uncrowded shore dive in the southern suburbs with easy parking and toilets, and a pleasant setting beneath the conservation park cliffs. It suits Open Water divers and snorkellers on calm days, and is a useful alternative when Port Noarlunga is busy. Because it faces west and is shallow, it is only worth diving on flat days.

Divers should also keep clear of rock fishers along the point and watch for fishing line in the kelp. After the dive, the boardwalk and interpretive trail through the conservation park make a worthwhile walk, and the beach kiosk is a convenient place to warm up.

From Adelaide drive south on Brighton Road/Lonsdale Road to Hallett Cove (about 30 minutes). Park at the Hallett Cove beach car park at the end of Heron Way or near the boardwalk (free, toilets nearby). Walk to the northern end of the beach and enter over sand and rock beside the point; the walk is short but the rocks are slippery.

Alternatively launch at O'Sullivan Beach ramp and run north about 10 minutes. The Hallett Cove Conservation Park boardwalk above the cove is a good vantage point to check conditions first.

Hallett Cove faces west-south-west and is open to the prevailing westerly and south-westerly winds and swell, which make entries rough and the water murky. Dive after several days of easterly (offshore) winds, early in the morning before the summer sea breeze. Tidal flow is minimal.

Visibility falls after rain because of the creek and stormwater outlets in the cove.

Enter beside the northern point and follow the reef edge north-west with it on your right shoulder at 4-7 m. Turn at half gas and return with the reef on your left.

No regular operator; listed by SDFSA as a metro shore dive and occasionally used by local clubs.