Seacliff Reef is widely considered the best natural reef dive off Adelaide. Several local sources, including the Scuba Divers Federation and the Sea Wolves, call it the best local site, and the Marine Life Network describes it as one of the best in Adelaide. It lies about 4 km off Seacliff in 12-15 m and, like the Glenelg reefs, is part of an ancient shoreline formed roughly 10,000 years ago when sea level was lower.

The reef runs north to south and rises only about 1 m above the sandy seabed, but it is longer and more complex than the Glenelg ledges, curving with gutters and ledges that give plenty of shelter. The rock is covered with sponges, bryozoans, ascidians and algae, and on a clear day the colours are vivid. Visibility is often better here than closer to Glenelg because the site is further from river and stormwater influence.

The fish are the headline. Sources describe thousands of fish, including notably large blue devils, and the site has a long reputation as a place where fish are used to divers. Boarfish, cuttlefish, leatherjackets, bullseyes, wrasse and blue groper are listed, along with nudibranchs, and the Marine Life Network records leafy seadragons.

No specific hazards are noted beyond those of any offshore boat dive. At 12-15 m, Seacliff Reef suits Open Water divers looking for their first offshore reef, photographers, and anyone wanting a long, fish-filled dive close to the city. It is also a good place to see what Adelaide's natural reefs looked like before the 2025 harmful algal bloom affected parts of the coast, as recovery is being monitored along the metro reefs.

Boat access only. Launch at the West Beach or Glenelg ramps (about 15-20 minutes south) or O'Sullivan Beach ramp (about 20 minutes north). The reef lies about 4 km offshore from Seacliff; the Marine Life Network notes it is marked by a tower.

Use a GPS mark and anchor in the sand along the reef's edge – there is no mooring. Keep a boat attendant aboard with a dive flag.

Like the rest of the metro coast, these sites face west into Gulf St Vincent and are best in offshore easterly winds, which are most common on summer and autumn mornings and on clear winter days. Westerly and south-westerly winds build chop quickly and make anchoring and recovery uncomfortable; the summer south-westerly sea breeze typically arrives late morning to early afternoon. Tidal streams in the gulf are modest but noticeable offshore on spring tides; neap 'dodge tide' days, when the water barely moves, give the easiest diving.

Visibility is usually better than at Glenelg because there is less river and stormwater influence, but drops after strong westerlies. Being further offshore, the deeper sites need a genuinely calm forecast.

Anchor beside the reef, then swim along its length with the ledge on one shoulder at 12-14 m, looking into gutters and under ledges. Turn at half gas and return along the reef top at 8-10 m to the anchor.

Occasional shop and club boat dives (Adelaide Scuba, The Dive Shack, Underwater Sports, Sea Wolves Dive Club); popular with private boats from West Beach and O'Sullivan Beach.