Michaelmas Reef is a long, low limestone reef lying a kilometre west of Michaelmas Island, about 2 km long and half a kilometre wide. Marine Life Network describes it as a favourite of underwater photographers: the reef rises only a few metres from the sand, with kelp-covered shallows on top and ledges, crevices and undercuts around the edges covered in sponges, gorgonians and colourful smaller invertebrates.

Because the depth stays in a narrow band of about 14-18 m, the reef suits relaxed, unhurried dives, and the limestone is riddled with small holes and overhangs where nudibranchs, cowries, feather stars, crabs and small reef fish can be found. The kelp canopy on top shelters schools of old wives, sweep and bullseyes, while blue groper, harlequin fish, western blue devils and boarfish work the ledges. Occasional Port Jackson sharks and wobbegongs rest on the sand edges.

There is no signature feature here – no wall or wreck – and that is part of the appeal: it is a site for slow exploration and macro photography, and for newer divers who want a straightforward, shallow profile away from the more exposed Breaksea sites. It is often dived by South Coast Diving Supplies when conditions on the outer islands are marginal, and can be combined with the Cheynes III, which lies nearby off Michaelmas Island. Experienced divers may find it less dramatic than the islands, but the invertebrate life repays a careful look, and in winter the sound's resident humpback and southern right whales can sometimes be heard underwater while you dive.

Albany is 418 km (about 4.5 hours) south-east of Perth via Albany Highway. Charter boats and private boats launch either from the Emu Point boat ramp (Emu Point Drive, 7 km north-east of the CBD, with a large trailer car park, toilets and a fish-cleaning station) or from the town ramp beside the Albany Waterfront marina in Princess Royal Harbour, which exits into King George Sound through the harbour entrance past Possession Point. Michaelmas Reef is about 5 km south-east of Emu Point (10-15 minutes by boat) and about 1 km west of Michaelmas Island, close to the Cheynes III wreck.

It is a broad reef, so boats simply anchor in sand along its edge on a GPS mark. There is no shore access.

King George Sound is sheltered from the Southern Ocean by Flinders Peninsula, Bald Head and Breaksea and Michaelmas Islands, which is why Albany can offer diving on days when the open coast is wild. Michaelmas Reef sits in the middle of the sound, open to wind chop from any direction but protected from ocean swell by the islands. It is best in light winds; strong south-westerlies and westerlies build a short, steep chop across the sound, and strong easterlies also make anchoring uncomfortable.

Summer mornings before the sea breeze are ideal. Visibility is moderate (10-15 m typical) and falls after winter rain.

Anchor on sand at the reef edge, descend and follow the reef margin at 15-18 m where the sponges and gorgonians are densest, then come up onto the kelp-covered top at 10-12 m for the return. A compass heading back to the anchor is useful because the reef is large and uniform.

South Coast Diving Supplies (Albany) – the town's dive shop; runs scheduled boat dives in King George Sound most weekends and on demand in summer/autumn, and issues HMAS Perth permits – used as a shallower photography and training dive.