Haystack Reef is one of the classic advanced dives of Yorke Peninsula. About 500 m off Haystack Island and running parallel to it for more than a kilometre, a limestone reef rises from sand at around 22 m to a top at about 10 m. The SDFSA describes a big wall running the length of the island with caves everywhere, swim-throughs, chasms and gorges, and The Dive Shack says it is enough for about ten distinct dives.

The wall is the colour highlight of the region. The SDFSA describes sponge and soft coral life so colourful – red, yellow and orange everywhere – that it rivals anything in the state, and gorgonian fans, ascidians and zoanthids crowd the vertical faces and cave roofs. Crayfish are abundant in the cracks, and the fish life is prolific: big schools of sweep, bullseyes and trevally, western blue groper, blue devils, boarfish and magpie perch.

Rays rest on the sand at the base, and seals from nearby colonies sometimes swoop along the wall. The topography rewards careful planning. The deeper sections at the wall base give the most dramatic structure and caves, while the reef top is ideal for the second half of the dive and a relaxed ascent.

Current is the main complication: it can run strongly along the reef, and operators insist on controlled ascents on a line or SMB. Haystack Reef is the logical step up for divers who have done the Innes shore sites and want a big, colourful wall. It suits Advanced Open Water divers with experience in current, and it is one of the dives that justifies the 3.5-hour drive from Adelaide.

From Adelaide drive about 300 km (3.5 hours) via Port Wakefield, Minlaton and Warooka to Marion Bay; Dhilba Guuranda-Innes National Park begins just west of the township (vehicle entry fee, pay online or at the Stenhouse Bay visitor centre). Launch at Marion Bay and run about 12 km west-south-west to Haystack Island (25-30 minutes); the reef lies about 500 m off the island and parallel to it. Find the wall with a sounder – it rises sharply from 22 m to about 10 m – and drop a shot on the sand.

The Dive Shack warns against free-water ascents because of current: ascend on a line or with an SMB and a tender.

The southern tip of Yorke Peninsula faces the open Southern Ocean and Investigator Strait, so south-westerly and southerly swell is the controlling factor: most exposed sites need swell under about 1.5 m and are best after several days of northerly or north-easterly winds, which blow offshore along this coast. Winter cold fronts bring big south-westerly swell and strong winds and can close the area for days. Summer afternoon south-easterly sea breezes make boat runs rough, so launch early.

Visibility is typically 10-20 m in settled conditions but drops sharply with swell-driven surge. Currents along the reef can be strong at times; aim for neap tides and plan for drift pick-ups.

Descend the shot to the sand at 20-22 m, then follow the wall with it on one shoulder, exploring caves, chasms and swim-throughs between 12 and 20 m. Turn on gas or current, rise to the top of the wall at 10 m for the last part of the dive, and ascend on the shot or an SMB – no free ascents in current.

Nitrox (EAN28-32) extends bottom time on the deeper wall base.

Adelaide shops (The Dive Shack, Diving Adelaide) and clubs include Haystack Reef on Innes boat weekends; private boats from Marion Bay. The Dive Shack notes it offers about ten distinct dives.