Birdrock Beach takes its name from Shag Rock, the flat-topped sandstone stack a short way offshore that is a roost for cormorants and other seabirds, and the reef around that rock is the dive. The Scuba Doctor lists it as a shallow reef dive of 1–6 m and notes seahorses, large crabs and eagle rays as the animals to look for. The seabed between beach and rock is a mix of sand, seagrass and low sandstone ledges; around the rock itself the reef is more broken, with crevices, small overhangs and weed-covered boulders where big-belly seahorses cling to the growth, decorator and spider crabs shelter, and octopus hole up under slabs.

Eagle rays and smooth stingrays cruise the sand edge, especially in the evening, and the usual eastern-bay fish – magpie perch, old wives, leatherjackets, zebrafish and hulafish – patrol the weed. Spearfishers know the site for whiting and flathead on the sand flats, and snorkellers use it more than scuba divers because the staircase from the Esplanade is a nuisance with tanks. That staircase is the main constraint: the source is explicit that it is not easy for divers carrying full kit, and the alternative access from the Morrisons Avenue lookout is steeper still.

Once in the water the dive is simple – out to the rock, around it, back – and well suited to Open Water divers on a calm, high-tide day with an easterly. On a westerly the beach forms a bar and rips and is not worth attempting. Birdrock is the southern-most of the Mornington cliff-coast shore dives before the Mount Martha gullies and gives a slightly different character from the piers: natural reef, an offshore stack for navigation, and rays rather than pier debris.

From Mornington follow the Esplanade south toward Mount Martha for about 3 km. Park in the small car park at 585 Esplanade, in the limited street parking on Birdrock Avenue and Shanns Avenue, or at the Morrisons Avenue lookout car park (steeper cliff access). A wooden staircase descends from the centre of the beach frontage; the source notes it is not easy to negotiate with full scuba gear but fine for snorkellers and spearfishers, so plan a second trip for tanks.

Enter from the beach and swim out toward Shag Rock, which lies a short distance offshore. Exit back onto the beach.

Birdrock Beach faces west and is exposed to westerly winds and waves; the source warns that strong winds produce waves high enough to form a bar and rips along the beach. Dive it at high tide with easterly winds, when the water is flat and there is depth over the inshore rock. Avoid westerly and south-westerly sea breezes, which arrive most summer afternoons, and anything above 15 knots from the north-west.

No current. Significant boat traffic passes between the beach and Shag Rock, so a dive-flag buoy is required rather than optional. Run-off after rain clouds the shallows.

Surface-swim from the beach toward Shag Rock towing a flag, descend on the inshore side in 3–4 m and circle the rock and its surrounding reef in 4–6 m, checking the ledges for seahorses and crabs. Turn at half gas, return toward shore across the seagrass and rubble, and surface close to the beach.

No regular operator; independent divers, snorkellers and spearfishers. Occasionally used by Peninsula clubs.