Port Willunga Reef is the shallow limestone reef that most divers use as a navigation line to the Star of Greece, but it is worth a dive in its own right. Diving Adelaide's guide to the wreck recommends swimming out to the reef and following it north at about 4 m, and notes that the adjacent reef holds uncommon nudibranchs, crabs and schools of small fish. Port Willunga was one of the colony's early grain ports.

The remains of the jetty built around 1867-68 still stand as pylons on the beach, and the soft cliffs behind are dotted with caves hand-dug at the same time to store fishing boats and gear – a much-photographed scene. The reef itself runs parallel to the shore, with ledges and holes covered in brown algae and kelp, sand channels and patches of seagrass. Marine life is typical of the shallow gulf coast: old wives, magpie perch, sweep, zebrafish, leatherjackets and wrasse, with crabs, nudibranchs and occasional cuttlefish.

Dolphins are sometimes seen in the bay. The combination of an easy beach entry, shallow depth and the historic wreck nearby makes this one of the most popular snorkel spots south of Adelaide in summer. The reef suits snorkellers, families and new divers on calm days, and photographers hunting nudibranchs.

It sits just north of the Aldinga Reef Sanctuary Zone. Leave the pylons and any historic material undisturbed, keep clear of swimmers, and use a surface marker because small boats and jet skis launch along this coast.

Port Willunga is about 45 minutes south of Adelaide. Park free in either of the two car parks near Jetty Road / the bottom of Star of Greece Road; toilets are at the bottom car park. Beach access ramps run either side of the Star of Greece restaurant.

Walk onto the beach and enter from the sand; the reef lies a short swim offshore, and the old jetty pylons are on the beach and in the shallows.

West-facing and shallow: dive only with low wind and low swell, after easterly winds, in the morning before the sea breeze. Summer usually brings the calmest conditions and the least sand movement. Low tide makes navigation easier but shallows the reef top.

Visibility drops quickly after westerlies, and after heavy rain when runoff from the cliffs and creeks reaches the bay.

Enter from the beach, swim out to the reef and follow its inside edge north at about 4 m toward the Star of Greece, then return along the reef's inside edge until you reach sand and head east to the beach.

Diving Adelaide – guided Star of Greece dives that follow the reef; otherwise independent divers and snorkellers.