Triangle Reef, also called South Triangle Reef, is the reef running out from Beaumaris Beach in front of the life saving club, named for the triangular navigation marker on its seaward end. It is the deepest of the Ricketts Point sanctuary sites, reaching 8 m at its outer edge, which gives it a little more variety than the platforms to the north-west: a shallow inner flat, a middle zone of gutters and low ledges at 3-5 m, and an outer edge with undercuts dropping onto sand. That extra depth, and the fact that the life saving club beach is a proper sandy beach with showers and toilets, makes it the most popular part of the sanctuary for actual scuba training as opposed to snorkelling, and on weekend mornings there are often several classes on the sand.

The fish are those of the whole sanctuary: snapper and zebrafish in numbers, flathead, dusky morwong, old wives and moonlighters, octopus in the holes, stingrays and fiddler rays on the sand and Port Jackson sharks under the outer ledges in the cooler months. The outer edge, being deeper and less trampled, has the best invertebrate cover, with sponges, bryozoans, sea tulips, nudibranchs and cushion stars. It is a very good night dive; the marker makes an easy turning point and the club beach a lit, obvious exit.

The reef is popular enough that Parks Victoria asks visitors to avoid trampling it, so enter and exit on the sand rather than across the rock, and keep fins up over the shallow flat. Table Rock and the Sea Scouts Jetty are a short swim or drive to the south-east for a second dive.

Park in the ticketed car parks off Beach Road at Beaumaris Beach near the life saving club (ample parking, machines take cards). Walk down to the beach, a carry of 50-100 m, and enter from the sand in front of the life saving club. The reef runs out from the beach toward the triangle marker; fin out on the surface until it is deep enough to descend.

Exit on the same sand; take care exiting near the triangle marker where the rocks are sharp. Showers and toilets are at the life saving club.

Best with offshore light northerly to south-easterly winds. Avoid moderate to strong onshore southerly through westerly to north-westerly winds, which raise chop across the shallow reef flats, stir the sand and make the rock entries unpleasant; if you see white water over the reef from Beach Road, go elsewhere (Quiet Corner is the fallback). Dive just before high tide for the clearest water and enough depth over the reef top, which is exposed or awash at low water.

Visibility 3-8 m on a good day, better in winter, poor for two or three days after rain. No swell. Boat traffic outside the swimming zone is constant in summer, so tow a flag.

Enter in front of the life saving club, fin out toward the triangle marker, descend at 2-3 m and follow the reef out to its deeper outer edge at 6-8 m, work along the edge and back through the gutters, turn at half gas and return to the club beach.

No commercial dive boat – shore site dived independently and by Melbourne dive shops for training and night dives (Scuba Culture in Cheltenham is the closest shop and uses the sanctuary regularly; Aquability and Melbourne Diving Services run club nights). Marine Care Ricketts Point runs guided snorkels in summer and Parks Victoria licensed tour operators run snorkel tours.