Koonya is an open ocean beach dominated by rock and reef rather than sand, lying between Sorrento and Blairgowrie on the back-beach coast, and it offers a shallow, rugged dive over intertidal and subtidal limestone with, as The Scuba Doctor notes, extensive deeper reefs further offshore. The listed depth is only 1–5 m, but the source's warning that the surge here can make this quite the washing machine to dive in should be taken literally: the reef is a broken field of platforms, gutters and low ledges directly exposed to the south-west, and even on a good day the water moves. The reward is a fish community that is unusually rich for the depth.

The source names goatfish, parrotfish (blue-throated and other wrasse), leatherjackets, herring cale, Port Jackson sharks, catsharks, old wives and cowfish, and the kelp and ledges also hold abalone, sea urchins, sponges and the small crustaceans that feed them. Rock lobsters are found in the deeper holes, and weedy seadragons occur along the kelp edge. Koonya is not a place to go deep; it is a place to move slowly through the gutters, look under every ledge, and enjoy the light and colour of the Bass Strait shallows.

It is diveable only under the standard back-beach rule – swell under about 1.5 m with periods of 10 seconds or more, after three or four days of northerly to north-easterly winds, with light northerlies on the day – and the exit over reef makes it worse than most when a swell arrives during the dive. Spray Point Caverns, 550 m to the south-east, is the deeper companion site. Koonya suits experienced divers and strong snorkellers who want a shallow reef with lots of fish on a glassy day, and it is a good place to learn to read the back beaches before attempting the deeper gullies.

From Point Nepean Road at Blairgowrie or Sorrento take Hughes Road south to the Koonya Ocean Beach car park. Wooden stairs at the western end of the car park lead down to the beach – about 100 m and a steep climb back. Enter from the sand between the inshore rocks at low tide and swim out through the gaps in the reef; the deeper reef lies offshore.

Exit at the same point on the beach; the source warns the exit can be a tough, slow walk to shore through shallow reef.

The back beaches face south-west into Bass Strait and are safe to dive only in rare flat conditions: The Scuba Doctor's rule of thumb is swell under about 1.5–2 m with periods of 10 seconds or more, usually only after three or four days of northerly to north-easterly winds, with light northerly winds on the day. Any southerly or westerly wind, or a fresh swell, makes the entries lethal. Dive around low tide when the limestone platforms are exposed and the gullies are sheltered, and abort if there is white water over the entry.

Rips and tidal streams near The Rip run even on calm days, and conditions change within an hour. Winter high-pressure systems bring the calmest spells; summer sea breezes rule out afternoons.

Enter at low tide through a sand channel, swim out over the inshore reef to the outer ledges in 4–5 m, then work parallel to the beach with the reef on one side, turning at half gas or when surge increases. Return through the same channel and time the exit between sets.

No regular operator. The Scuba Doctor (Rye) and Peninsula clubs run occasional guided shore dives when conditions allow; otherwise experienced private groups only.