Marek's Reef is a classic 'junk reef', built in the days when dumping scrap on the seabed was seen as the easiest way to create fish habitat. The Marine Life Society lists car bodies, old boilers, gantries, tyre pyramids, washing machines, stoves and refrigerators, all deposited in about 12 m on a sand bottom south of Whyalla. Decades of growth have turned the scrap into a surprisingly rich reef.

The Society describes thick growths of sponges, ascidians and soft coral on the structures, and schools of whiting and snapper around them. Leatherjackets, magpie perch, bullseyes and tommy ruff shelter in the car bodies and appliances, blue swimmer crabs and octopus hide beneath, and cuttlefish are common in winter. The dive is a slow exploration of odd shapes – a boiler here, a gantry there, a fridge covered in sponges – and it rewards photographers who enjoy the contrast of colourful life on industrial debris.

Like all upper-gulf boat sites, it is affected by tide: plan for slack water, when visibility can be good. The Marine Life Society describes the reef as immediately south of the Leeton wreck, but the published coordinates place Marek's several kilometres north-north-west of the Leeton; divers should rely on the GPS positions. Marek's Reef suits Open Water divers with boat access and an interest in artificial reefs, and pairs with the Leeton tug for a two-dive morning out of Whyalla.

Local fishers also target the reef, so expect lines and anchored boats on weekends; arrive early and keep clear of anglers' gear. Gloves help when steadying yourself near the scrap metal, which is sharp and flaking in places, and nothing should be entered – old car bodies and appliances can collapse.

Whyalla is about 390 km (4-4.5 hours) from Adelaide via Port Wakefield, Port Augusta and the Lincoln Highway, or a 45-minute flight. Launch at the Whyalla marina ramp and run about 7 km south to the reef (15 minutes). Published WGS84 position: S 33° 05.722', E 137° 36.394'.

Anchor or shot beside the structures rather than on them, and dive at slack water.

Upper Spencer Gulf has no ocean swell; wind and tide control conditions. Strong southerly and south-westerly winds blow straight up the gulf and raise a short, steep chop, and northerlies stir the shallow water along the northern shores. Tides are large for South Australia (over 2 m on springs) and run hard around Point Lowly and in the shipping channels, so boat sites should be dived at slack water – visibility is often excellent (15-20 m+) at slack and murky when the tide runs.

Winter (May-August) brings the calmest mornings and cold water (11-13°C); summer water reaches the mid-20s but afternoon sea breezes are common.

Descend the shot, then swim a circuit between the car bodies, boilers and tyre pyramids at 10-12 m, looking into the structures for fish and crabs. Return to the shot before the tide picks up.

Whyalla Dive Shop (Why Dive) can arrange boat dives; otherwise local divers and fishers with boats.