The big jetty at Ardrossan was built by BHP to load dolomite quarried nearby for its steelworks, and it has since also served as a grain-loading facility. It runs far out from the shore north of the town and reaches about 15 m at its head, making it a completely different dive from the shallow town jetty. The Dive Shack and SDFSA both describe it as a moderate boat dive, and both single out the same feature: huge schools of fish congregate at the end.

The massive piles and loading structure offer a lot of hard surface and deep shade, and they are colonised by sponges, soft corals, ascidians and hydroids. Around the head, schools of yellowtail scad, tommy ruff, trevally and old wives mill in the shade, with snapper, sweep and leatherjackets among them, while Port Jackson sharks, stingrays and blue swimmer crabs work the bottom. Smaller life – nudibranchs, crabs, octopus – is found on the lower piles.

Because it is a working facility there is no public shore access, and the jetty can only be dived from a boat when no ship is in port. That restriction, plus the need for a boat, means it is rarely dived, mostly by locals and club members. Visibility in the upper gulf is often limited, but the depth means the jetty head is less affected by surface stirring than the shallow jetties.

For divers with a boat who have done the town jetty, the BHP jetty is the more interesting deeper option, and it can be combined in a day with the Zanoni wreck (permit required) or the Ardrossan Barge further out in the gulf. It suits Open Water divers comfortable at 15 m in variable visibility.

Launch at the Ardrossan boat ramp below the town (about 150 km from Adelaide) and run north about 1.5 km along the coast to the outer end of the loading jetty – a 5-10 minute trip. There is no public shore access to this working jetty. Anchor clear of the berth and loading gear, fly a dive flag, and only dive when no vessel is berthed or approaching; check shipping schedules with the port if unsure.

This coast faces Gulf St Vincent, so onshore easterly, north-easterly and south-easterly winds ruin it: 15 knots from the east stirs the fine sediment and drops visibility to a metre or two, and a strong south-easterly adds chop and surge. Westerly and south-westerly winds blow offshore and give the flattest, clearest water, best after a day or two of settled weather. There is no ocean swell inside the gulf.

Tides are modest (1-2 m, with 'dodge' tides of little movement), but shallow jetties are easier around high water. Autumn is calmest; summer south-east sea breezes build in the afternoon, so dive mornings. The jetty head is more exposed to the open gulf than the town jetty, so wind chop over 15 knots makes the boat approach uncomfortable.

Ship scheduling overrides weather.

Anchor off the outer end, descend to the sand at 12-15 m and circuit the head of the jetty, where the fish schools concentrate, working the piles for crabs and small life. Ascend on the anchor line for a safety stop at 5 m.

No regular operator; dived by Adelaide club members and locals with private boats from Ardrossan ramp. SDFSA lists it as a boat dive.