Port Noarlunga Reef is Adelaide's premier shore dive and the most dived site in South Australia. The reef is a long, fairly flat-topped limestone ridge about 1.6 km long running parallel to the coast a couple of hundred metres offshore, exposed at low tide and connected to the beach by a 300 m wooden jetty. Wikivoyage aptly describes it as looking like a collapsed wharf, with blocks pushed into the sea on each side.

The reserve was declared in 1971 as South Australia's first aquatic reserve and is now a sanctuary zone within Encounter Marine Park, receiving an estimated 170,000 visitors a year including thousands of divers. The reef has two distinct sides. The inside, facing the beach, is a sheltered lagoon in about 5 m with a jumble of large blocky boulders near the jetty, overhangs and gaps, sparse kelp and other seaweeds, crustose corallines and sponges.

The outside faces the open gulf, is more exposed and slopes to about 8-10 m. The reef is divided into northern and southern sections by the Gap, a channel that reaches about 20 m and carries a strong current on big tides. More than 200 species of plants and animals and over 50 fish species have been recorded.

Old wives, silver sweep, moonlighters, zebrafish, drummer, magpie perch and wrasse are everywhere; blue devils, cuttlefish, wobbegongs and stingrays are regular, and over 50 species of nudibranch have been logged. From November to January Port Jackson sharks gather to breed and lay eggs among the ledges. Seahorses, pipefish and occasional leafy seadragons in the northern weeds reward careful searching, and dolphins and whales pass occasionally.

The jetty stairs, sheltered inside, easy navigation and good facilities make Port Noarlunga the default training site in Adelaide and an excellent night dive. It suits everyone from snorkellers to photographers, while the outside and the Gap give experienced divers more to explore.

Port Noarlunga is about 35-40 minutes' drive south of Adelaide via the Southern Expressway or Main South Road; turn off to the Esplanade at Port Noarlunga. Park at the base of the jetty (limited spaces) or in the larger car park about 100 m away; many divers use a trolley for the 300 m jetty walk. The jetty has wide non-slip stairs, handrails and several platforms for different tide levels: the first stairs enter in about 3 m, and the final stairs at the end, beside the reef, enter in about 6 m and are the most popular.

The middle stairs are difficult and unusable at low tide. Boats can also launch at O'Sullivan Beach, 10 minutes north.

The reef runs parallel to the shore and shelters the inside lagoon from the prevailing westerly and south-westerly swell, so the inside can be dived when the outer reef is rough; even so, strong westerlies or any swell over about 1 m make the beach entry surfy and the water murky. Best conditions come after several days of offshore easterly winds, on summer and autumn mornings before the south-westerly sea breeze. Tide matters: local guides warn of strong current when the difference between high and low tide exceeds about 1 m, especially through the Gap, so plan around high slack water and prefer neap (dodge tide) days.

Visibility is poorer after rain, when the Onkaparinga River discharges just south of the reef.

Enter from the end stairs, descend beside the reef and follow it north or south with the rocks on one shoulder at 5-7 m; on the inside the underwater trail markers provide a route. Experienced divers can go through the Gap to the outside of the reef (to 8-10 m, 20 m in the Gap) on slack water. Turn at half gas and return with the reef on the other shoulder, surfacing at the jetty stairs.

Diving Adelaide (Glandore) – regular guided shore dives, courses and Port Jackson shark tours; Adelaide Scuba (Glenelg North), Underwater Sports (Edwardstown) and The Dive Shack – frequent training and club dives; heavily used by clubs and independent divers year-round.