Penneshaw's jetty is the first thing most visitors see of Kangaroo Island – the SeaLink ferry from Cape Jervis docks beside it. Built in 1901 and extended in 2012 to take cruise-ship tenders, it also supports recreational diving, with gorgonian coral documented on the structure. The Marine Life Network describes it as a 6 m pylon dive that is 'shallow, safe and easy', excellent for photography and better at night.

The pylons carry gorgonians, sponges and ascidians, and the sand and weed around them hold goatfish, trevally, salmon and drummer, with octopus emerging on night dives. Backstairs Passage water is often clearer than Nepean Bay's, and cuttlefish, leatherjackets and occasionally seadragons turn up. Penneshaw is also home to a declining colony of little penguins, which nest along the foreshore – keep lights low and do not disturb them on night dives.

The ferry is the main hazard: never dive near the berth when a vessel is due, stay under the jetty's outer structure only when you are sure of the timetable, and tow a float. Hog Bay, where the town began and where Baudin's crew carved Frenchman's Rock in 1803, is right beside the jetty and has its own reef snorkel (separate row). The jetty suits beginners, photographers and anyone wanting a dive before driving on across the island. Fill cylinders in Kingscote or bring them from the mainland on the ferry, as there is no dive shop in Penneshaw. The jetty's timber piles and the 2012 extension offer different surfaces for growth, so it is worth exploring both sections.

Take the SeaLink ferry from Cape Jervis to Penneshaw (45 min). The jetty is in the centre of Penneshaw beside the ferry terminal; park in the town near the foreshore (not in ferry marshalling lanes), gear up and enter from the beach beside the jetty or from the jetty steps. Check ferry and cruise-tender times and stay clear of the ferry berth – ask the terminal about any restrictions.

It makes an easy dive on the day you arrive.

The Dudley Peninsula sites lie on Backstairs Passage and Eastern Cove, sheltered from the prevailing south-westerly swell but swept by strong tidal streams through the passage. Dive around slack water, particularly near headlands and islands; wind against tide creates steep chop. Easterly and north-easterly winds make Penneshaw and Hog Bay choppy, while south-easterlies affect Antechamber Bay and Cape Willoughby.

Summer and autumn bring the calmest days; winter westerlies are usually fine on this side of the island.

Enter away from the ferry berth, descend to the sand at 3-5 m, and work slowly along the pylons checking for gorgonians, nudibranchs and goatfish; at night look for octopus. Return along the other side.

No local operator in Penneshaw; Kangaroo Island Dive & Adventures (Kingscote) – guided dives and advice (confirm current trading). Adelaide operators occasionally include it on KI trips.