Edithburgh is the jetty that South Australian divers measure every other jetty against, and many consider it the best jetty dive in the country. Built in 1873 to ship salt and grain, the structure runs about 170 m out from the foreshore and is 12 m wide, with a forest of timber and steel piles standing in 2-9 m of water over a sand and rubble bottom. Over 150 years the piles have been coated in a dense sleeve of sponges, ascidians, bryozoans, hydroids and soft corals in orange, purple, yellow and red, and this growth is the foundation of an extraordinary density of small life.

The site's reputation rests on macro. Nudibranchs occur in dozens of species, and the jetty is one of the most reliable places in the state for tasselled, smooth and prickly anglerfish, which sit motionless among sponges of the same colour. Pyjama squid and southern dumpling squid bury in the sand by day and hunt by night, big-bellied seahorses and several pipefish species anchor to the piles, and blue-ringed and sand octopus move through the debris.

Port Jackson sharks and catsharks rest under the jetty, giant cuttlefish and southern calamari hover in the shade, and on the low limestone reef about 50 m north of the stairs leafy seadragons are regularly found in the weed. Dolphins and sea lions occasionally visit. Night diving is where Edithburgh earns its top-ten Australian ranking: decorator crabs, hermit crabs, shrimps, basket stars and hunting octopus emerge, and the squid put on colour displays in torchlight.

Because the depth rarely exceeds 9 m, a single tank lasts well over an hour, and it is common for photographers to spend two or three dives on the same few piles. The dive suits everyone. Newly certified divers can do it unguided in calm weather, snorkellers can work the shallow end, and experienced photographers return for years.

Its sheltered position also makes it the fallback when the south coast of the peninsula is blown out, though it is itself vulnerable to easterly winds. Weekend fishing pressure is real, so plan around anglers on the T-head.

From Adelaide take Port Wakefield Road and the Copper Coast/Yorke Highway south through Ardrossan, Port Vincent and Stansbury (roughly 225 km, 2.5-3 hours), or turn off at Minlaton and head east. In Edithburgh follow Edith Street down to the foreshore; the jetty is at the end of the esplanade beside the tidal swimming pool. Park on the jetty approach or the foreshore car park directly beside the stairs, so the gear carry is under 30 m.

Descend the stairs on either side of the jetty near its base and fin out under the structure; the northern reef is reached by swimming roughly 50 m north from the stairs. Air fills are available in town (Edithburgh Motors) and at the caravan park.

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. Local divers summarise Edithburgh visibility by wind direction: north average to poor, north-east poor, east atrocious, south-east generally OK, south good to great, south-west and west really good, north-west usually OK.

Enter by the stairs, drop to the sand at 3-4 m and work slowly out along one side of the pylons searching the sponge-covered piles and debris for anglerfish, pyjama squid and seahorses. At the T-head (7-9 m) cross under and return along the other side. With air to spare, head about 50 m north of the stairs to the low reef for leafy seadragons and cuttlefish before returning to the stairs; the whole dive is shallow enough that no formal safety stop depth is hard to hold.

Diving Adelaide runs regular guided weekend and night-dive trips from Adelaide; The Dive Shack, Adelaide Scuba and Glenelg Scuba run club trips several times a year. Most divers visit independently, particularly photographers doing multiple night dives over a weekend.