The shoreline of Rivoli Bay between Southend and Beachport is fringed by shallow limestone reef that the Marine Life Network describes as reef-based fish life, with leafy seadragons and southern rock lobster under the ledges, and depths of about 5 m. Post Office Rock near Beachport is the named feature locals point to. The same source notes the area is very exposed to bad weather, good for night dives in calm conditions, and popular with anglers.

This is typical Limestone Coast reef: flat and ledged limestone cut into gutters, overhangs and small caves by the swell, covered in brown algae and kelp with sponges under the overhangs. Rock lobster – the backbone of the local fishing industry – shelter in the ledges, and leafy seadragons may be found drifting among the weed. Wrasse, sweep, leatherjackets and small reef fish are common, and there are sandy patches with rays and flathead.

There is little published diver-specific information, so treat it as exploratory. The key is conditions: the reef only settles after several calm days, and the shallow water means surge is felt right to the bottom. When it is flat, it offers relaxed, shallow reef diving and snorkelling close to town and a good complement to the jetty. Note that rock lobster fishing is heavily regulated in South Australia and the season is closed in winter; divers who intend to take lobster need the appropriate licence and pot/snare rules. It suits confident shore divers who can read the sea. Combine it with the jetty for an easy two-dive day in Beachport, with lunch in town between dives.

Beachport is about 85 km north-west of Mount Gambier via Millicent. The reef runs along the Rivoli Bay shoreline towards Southend (about 20 km by road around the bay). Access points are informal: park along the foreshore roads or at beach car parks, carry gear across the sand and enter from the beach or low rock platforms, choosing a spot with an obvious exit.

Ask locally for the Post Office Rock entry; Bowman Scenic Drive gives views of the coast.

The Limestone Coast faces the full Southern Ocean, and prevailing south-westerly swells of 2-4 m are the norm, especially May-October. Shore and boat dives need a genuine calm spell: swell under about 1 m, light winds, ideally northerly or north-easterly offshore breezes, and a few settled days for visibility to recover. Summer south-easterly sea breezes build most afternoons, so dive early.

Heavy winter rain brings tannin-stained run-off from drains and creeks that reduces visibility near shore. Autumn (March-May) usually has the most calm days and the best visibility. The marine life network describes the Beachport reefs as very exposed to bad weather.

Enter from the beach at a sheltered gap, fin out over sand to the reef edge at 3-5 m and work along the ledges looking for rock lobster and seadragons, turning at half gas to return to the same entry.

No regular operator – independent shore diving; fills in Mount Gambier.