Racecourse Bay lies immediately west of Port MacDonnell, and the Marine Life Network lists it alongside the breakwater as the town's limestone reef option, at 2-5 m. It gives a more natural reef dive than the harbour, at the cost of more exposure.

The reef is low, ledged limestone with brown algae and kelp, sand gutters and small overhangs. Expect wrasse, sweep, leatherjackets, magpie perch, old wives and small reef fish, rock lobster in the ledges and the usual southern invertebrates – sea stars, urchins, sponges and abalone. Seadragons are possible in the weed. The shallow depth gives plenty of light on sunny days and makes it a good snorkel, but surge is felt all the way down.

The Port MacDonnell coast is also the heart of the lobster industry, and the rocky shores east at Cape Northumberland shelter lobster and little penguins. There is little formal dive documentation for Racecourse Bay itself, so it is best treated as an exploratory, calm-day site; talk to locals or the Mount Gambier dive shop for current entry points. It suits confident shore divers and snorkellers looking for easy reef close to Mount Gambier, and pairs well with a breakwater dive on the same day. Because there is no local dive shop in Port MacDonnell, fill cylinders in Mount Gambier before driving down, and check the swell forecast rather than relying on the view from town – the harbour can look calm while the open bays are still surging. Autumn mornings with light northerly winds are the pick. Snorkellers should stay close to the beach and away from any rip channels.

From Port MacDonnell (28 km south of Mount Gambier) drive a couple of kilometres west along the coast road to Racecourse Bay, with views east back to the town. Park at the roadside/foreshore pull-offs, carry gear down to the beach and enter from the sand or low rocks at a sheltered spot, noting your exit. No facilities at the bay; Port MacDonnell has toilets and cafes.

The Limestone Coast faces the full Southern Ocean, and prevailing south-westerly swells of 2-4 m are the norm, especially May-October. Open-coast 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 run-off that reduces visibility near shore. Autumn (March-May) usually has the most calm days. Racecourse Bay is more exposed than the breakwater; dive it only when the swell is small.

Enter from the beach, fin out over sand to the limestone reef at 2-5 m, follow the ledges along the bay and return to the same entry at half gas.

No regular operator. Fills at Dive Experience, Mount Gambier.