Rosebud Reef is a small natural oasis on the wide sand plain of the southern bay: a ridge of rock about 250 m long lying north-west to south-east, standing two or three metres proud of the seabed a kilometre off Rosebud in 4–10 m. In an area where almost all diving is under piers, it is one of the few pieces of open-water natural reef reachable in minutes from the Rye ramp, and it carries a disproportionate amount of life for its size. The rock is covered with sponges, ascidians and encrusting invertebrates, sea urchins graze the ledges, and small ledges along its flanks shelter wrasse, leatherjackets, magpie perch and seahorses.

The source notes that the concentration of small life draws harmless sharks – wobbegongs resting under the overhangs and, at times, broadnose sevengill sharks cruising the edge, which for many Port Phillip divers is the main reason to visit. Scallops lie on the surrounding sand, and rays, flathead and the occasional snapper patrol the reef margin. The dive is simple: follow one side of the ridge to its end, cross the top and return along the other side, with no current and modest depth allowing a long, relaxed circuit.

It is a good first boat dive for divers stepping up from the piers and an excellent kayak dive in flat weather. The difficulty is finding it – published positions vary by a few hundred metres and nothing shows on the surface, so a sounder and patience are needed. Rosebud Reef has no operator running trips and is largely the preserve of private boats and clubs, which keeps it uncrowded.

It suits Open Water divers with boat access, photographers wanting sharks and sponges in shallow water, and anyone who wants to see what the bay's natural rocky bottom looks like away from man-made structure.

Launch at Rye boat ramp (5 km west) or the Anthonys Nose ramp at Dromana and motor to the marks about a kilometre off Rosebud beach – 5–10 minutes. Several published positions differ by a few hundred metres (The Scuba Doctor, Dive Victoria and John Lawler marks), so run a sounder pass to find the 2–3 m rise. Anchor on sand beside the reef and descend the line.

Kayak divers occasionally paddle out from Rosebud in flat conditions; it is a 1 km paddle each way.

Open to northerly and westerly winds, which build a chop across the southern bay and cloud the shallow sand; best on light southerly to easterly winds and flat water. There is no meaningful current this far east of the Heads. Visibility is usually reasonable and improves in winter.

The site lies in the path of boats running between Rye and Dromana, so a flag on the boat is essential and a surface marker should be carried.

Descend the anchor line to the sand at 8–10 m, find the reef edge and follow it north-west along one side for about 250 m, cross over the top and return along the other side, checking ledges for wobbegongs and the sand for scallops. Ascend the line with a short stop.

No regular charter; private boats, kayak divers and Peninsula clubs. The Scuba Doctor and Extreme Watersport can advise on marks.