Seal Island is a small granite outcrop in the south-western part of King George Sound, best known to divers as the neighbour of the HMAS Perth, which lies 500 m to its south-west. It is a worthwhile dive in its own right, and a relaxed shallow option after a deep wreck dive.

The reef is shallowest on the western side, from about 5 m, and deepens toward the east to around 20 m. Marine Life Network lists an unusually broad mix of life for such a small site: plate corals on the rock, western blue devils, pineapple fish in the ledges, scorpionfish, queen snapper, yellowtail kingfish, blue groper and harlequin fish, along with sea dragons and nudibranchs. As the name suggests, seals occasionally appear; the island is used as a haul-out by New Zealand fur seals and the odd Australian sea lion.

The granite forms boulders, overhangs and small gutters rather than big walls, with patches of kelp and seagrass on the surrounding sand where cuttlefish, squid and Port Jackson sharks are found. Pineapple fish and blue devils make it a favourite night dive – the pineapple fish's light organs glow in torchlight – and the sheltered position means night trips can often go ahead when the rest of the coast is rough.

Seal Island suits all levels: new divers can stay on the shallow western reef, while experienced divers can explore the deeper eastern side. Combined with the Perth it makes an easy double-dive morning from Albany, and snorkellers can enjoy the shallow reef on calm days.

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. Seal Island is about 7-8 km (15-20 minutes) from the Princess Royal Harbour ramp, just north-east of the HMAS Perth moorings, so charters commonly make it the second dive of a Perth trip.

Anchor in sand off the western side for the shallow reef or off the eastern side for the deeper terrain. There is no landing.

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. Seal Island is in the protected south-western corner of the sound and is diveable in most conditions; Marine Life Network advises avoiding it in heavy easterlies, which blow directly across the sound onto the site. Westerlies are comfortable here.

Visibility is usually similar to or slightly better than on the Perth (5-15 m) and drops after winter rain.

Anchor off the western side, descend to 5-8 m and circle the island clockwise, dropping deeper along the eastern side toward 15-20 m, then return shallow along the northern side. At night stay shallow on the western reef where the invertebrates are easiest to find.

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 second dive after the HMAS Perth.