South Brig Rock is a small island near Grassy that the Marine Life Network guide rates 7 out of 10. Its eastern side is surrounded by sunken outcrops, with shallow rocks at about 5 m that are good for crayfish, challenging swim-throughs close to the island and deeper, safer water further out on the rocks to 18 m. Cracks support gorgonian fans and small marine life, and the seaweed growth is luxuriant.

The guide describes very large crayfish of 3.5-4.5 kg and notes that they fight hard. Sea sweep, old wives and long-snouted boarfish are the common fish. The site is popular in westerly weather, but the exposed rocks pound in heavy swell.

King Island's reefs are best known to divers for their crayfish, which grow large in the cool, nutrient-rich Bass Strait water, and for sandstone and granite ledges covered in gorgonians, zoanthids and sponges. The Marine Life Network descriptions date from when King Island Dive Charters operated from Grassy; with no current operator, these sites are now visited only by divers who organise their own boat, and fishing pressure has reduced crayfish numbers since.

Recreational rock lobster and abalone fishing in Tasmanian waters needs a licence and is subject to seasons, size and bag limits. The east coast around Grassy is the reliable side of the island when westerly swell closes the west coast, and the island's lack of a chamber means aeromedical evacuation for any diving injury, so conservative dives are the rule.

This is a site for self-sufficient visiting divers with their own boat and a local contact; there is no one on the island currently guiding dives here, and the position given is an estimate from the published description.

King Island is reached by air from Melbourne (about 50 minutes), Burnie/Wynyard or Launceston; there is no passenger ferry, so divers fly in and hire a vehicle at the airport near Currie. Currie, the main town, is on the west coast; Grassy (with its harbour and boat ramp) is on the south-east coast about 30 minutes' drive away. Roads to the coast are a mix of sealed and gravel.

South Brig Rock is a short run (about 10 minutes) from the Grassy Harbour ramp on the south-east coast. Divers anchor or drop on the eastern side.

King Island sits in the path of the Roaring Forties, and its west coast (Currie, Netherby, Cataraqui, Brahmin) takes the full force of the prevailing westerly and south-westerly swell; these sites are diveable only after long calm periods or in easterly weather, which is most common in late summer. The east coast around Grassy is sheltered in westerlies and becomes the fallback. Strong tidal streams run around the island's capes after gales.

South Brig Rock is popular in westerly weather; avoid the shallow rocks and swim-throughs in heavy swell.

Drop on the eastern side and explore the sunken outcrops from 5 m out to 18 m, visiting the swim-throughs near the island only in calm conditions; finish on the deeper, safer outer rocks if swell is running. Turn the dive at half gas (thirds where current or overhead sections are involved), deploy an SMB before surfacing for the live-boat pick-up, and complete a 3-minute safety stop at about 5 m where depth allows.

No dive shop or charter currently listed on King Island (Underwater Australasia has no listings); the King Island Dive Charters/Dive Centre referred to in older guides no longer appears to trade. Visitors must bring their own gear and arrange cylinders and a boat locally (hire weights/tanks on the island where possible to reduce air freight). Verify any current operator before travelling.