The Dredge is the best-known boat dive off Adelaide and, in the words of the local Scuba Divers Federation guide, arguably the best fish dive off the metropolitan coast. The vessel is the South Australian, a self-propelled cutter-suction dredge built in Holland in 1911 and about 35 m (133 ft) long and 7 m wide. She spent decades working for the state, including clearing sand from the Port River, before being scuttled in January 1985 as part of a deliberate artificial reef program alongside the Glenelg Barge (sunk 1984) and the older Glenelg Tyre Reef.

She sits upright on a flat sand and silt bottom in about 20 m, with her deck around 15 m, which puts the whole wreck within reach of Advanced divers on air. After four decades underwater, the steel is thickly covered in sponges, ascidians, bryozoans, soft corals and anemones, and the structure concentrates fish in a way the surrounding bare seabed cannot. Large schools of bullseyes hang in the shadow of the hull, and old wives, blue devilfish, morwong, magpie perch, leatherjackets, strongfish and boarfish are common.

Wobbegongs rest on and under the wreck, cuttlefish are frequent, and stingrays sit in the sand alongside. The wreck is still recognisably a ship: the cabin rooms and the pump hold can be entered by trained wreck divers, but the interior is silty and some deeper spaces around the boiler and engine room are considered unsafe because of deteriorating steel. Most divers are happy on the outside, where two or three laps at different levels fill a 35-minute dive.

A trail of star droppers links the Dredge to the nearby Barge, so on a quiet tide it is possible to see both wrecks on a single dive. The Dredge suits newly Advanced divers wanting their first real wreck, photographers after fish schools and encrusting growth, and anyone looking for a reliable metro boat dive close to town. It is also a good benchmark site for the health of Adelaide's offshore reefs after the 2025 harmful algal bloom.

Boat access only. Adelaide Scuba runs its charters from its shop on the Patawalonga at Glenelg North, with the boat leaving through the Patawalonga/Holdfast Shores entrance; private boats launch at the West Beach boat ramp (Barcoo Road end of the West Beach dunes, large trailer park, fee payable) or the Glenelg (Holdfast Shores) ramp. From Glenelg it is a run of about 10-20 minutes due west in flat water.

Use GPS marks: the sites are low-relief and cannot be seen from the surface, and there are no public moorings, so anchor in sand off the structure and leave a boat attendant with a dive flag up because charter and fishing traffic is steady on weekends.

The metro coast faces west into Gulf St Vincent, so the rule is simple: offshore easterly winds flatten the sea and clear the water, while westerlies and south-westerlies build a short, steep chop and stir up the silty bottom. In summer the south-westerly sea breeze usually arrives by late morning or early afternoon, so boats aim to be back in by lunchtime. Northerlies are workable when light.

The gulf has a mixed, small-range tide with 'dodge tides' (neap periods when the water barely moves) that give the easiest diving; strong spring tides can run noticeably across the offshore wrecks. Visibility drops for several days after strong westerly blows and after heavy rain when stormwater and Patawalonga/Torrens outflow reach the coast.

Anchor or drop a shot on the sand beside the hull and descend to the main deck at about 15 m. Circuit the outside of the hull at the sand (20 m) first, then come up to deck level and work back along the superstructure and the cabin area. Trained wreck divers can look into the open cabin rooms and pump hold; the boiler and engine spaces are silty and not recommended.

If current is light, follow the star-dropper line across to the Barge for a two-wreck dive, then return to the anchor line for a safety stop.

Depth suits air or EANx 32 for longer bottom times. Penetration only with wreck training, a guideline and redundant light; interior silts quickly.

Adelaide Scuba (Glenelg North) – scheduled 'Dredge and Barge' double-dive boat trips, typically weekends in season; Underwater Sports (Edwardstown) and The Dive Shack (Glenelg) – periodic club/shop boat dives; also dived regularly from private boats out of West Beach.