The old Rapid Bay jetty built the site's legend. Opened in 1942 to load limestone from BHP's quarry via a conveyor, it ran about 450 m out from the shore – turning slightly right at the 360 m mark, where timber piles give way to steel – to a 200 m T-shaped wharf with six multi-pile dolphins. The seabed drops from about 5 m to 8 m at that point, and the end of the wharf reaches 10-12 m at high tide.

Divers knew its features by name: the Tee, the shaded 'Cathedral' at the junction where large fish schools gathered, the A-frame on one dolphin, and the grid, a large fender lying on the bottom. Decades without maintenance turned the structure into an extraordinary artificial reef. The piles were heavily covered with sponges, ascidians, bryozoans and soft corals in many colours, with seaweeds on sunlit surfaces, and rubble and detritus between the piles sheltered a huge range of fish and invertebrates.

Leafy seadragons lived beneath the jetty and in the surrounding seagrass, and the site became a pilgrimage for underwater photographers from around the world. The jetty had been deteriorating for years, and in May and June 2025 storms caused further collapse. The state government imposed a 20 m exclusion zone for divers, swimmers and boats in June 2025, with buoys and signs, and an engineering assessment is under review.

Local operators and divers have campaigned to reopen access, warning that businesses depend on it, but at the time of writing the zone remains. Until it is lifted, divers should not enter the zone and should instead dive the new jetty and seagrass beds, where leafy seadragons are still regularly found.

Rapid Bay is about 1 hour 30 minutes (about 100 km) south of Adelaide via Main South Road; turn right at the Rapid Bay turn-off past Delamere and follow the road down to the bay. Park in the long, narrow unsealed car park as close as 60 m from the new jetty (a ground sheet helps when gearing up). Walk the new concrete jetty about 240 m to its outer end – a handcart or trolley is useful – where a large steel staircase with handrails descends to a landing at about low-tide level.

Historically divers swam from the landing across to the old jetty (about 50 m, marked underwater with star droppers) and along it to the T-section. Since June 2025 all divers, swimmers and vessels must stay at least 20 m from the old jetty; buoys and signs mark the zone. Check the Department for Infrastructure and Transport's Rapid Bay page for the current status before planning a dive.

Rapid Bay faces north, so it is sheltered from southerly and south-westerly weather but exposed to winds and swell from the north-west through north-east. January to April is the best period, when the prevailing pattern blows offshore (south-easterlies). Strong northerlies make the stairs rough and stir the bottom; visibility below about 5 m makes navigating between piles difficult.

Tidal currents are usually slight, although a westward drift has been noted on a rising tide with no wind, and the ranger service warns of strong tides at times; neap dodge tides are easiest. The site is diveable year-round when winds are southerly. The 2025 harmful algal bloom affected the area; check recent reports.

Currently not diveable. Formerly: enter at the new jetty stairs, cross to the old jetty, follow it out to the T-section (5-6 m opposite the entry, deepening to 8-10 m and 10-12 m at the end), explore the Cathedral, the A-frame and the grid, and return along the other side.

Closed to divers since June 2025 (20 m exclusion zone). Before closure it was the main site for Sea Dragon Dive Lodge, Diving Adelaide, Adelaide Scuba, Underwater Sports and many clubs.