Dive glossary

Australian diving has its own vocabulary. These are the terms used across the site pages and by operators around the coast.

Bommie: An isolated coral or rock outcrop rising from the seabed, often to near the surface. From the Aboriginal word bombora. Steve's Bommie, Heron Bommie and Manta Bommie are all single pinnacles surrounded by sand or deeper reef. Best Great Barrier Reef dives →
Bombora (bombie): A submerged reef or rock over which waves break, especially in swell. On the NSW coast a bombora is a hazard to boats and a marker for good fish life below it.
Slack water: The short period at the turn of the tide when current stops before reversing. Port Phillip Heads, Fly Point, the Gold Coast Seaway and Darwin Harbour are dived only on slack, which may last from ten minutes to an hour depending on the site and the tide.
Dodge tide: A South Australian gulf phenomenon: roughly every fortnight the semi-diurnal and diurnal tides cancel out and there is almost no tidal movement for about a day. The calmest conditions for the gulf jetties.
Neap tide: The tides of smallest range, occurring near the first and last quarter of the moon. Darwin, Broome and Mackay diving happens on neaps, when the current is weakest and the water clearest.
Gutter: A sand-floored channel between reef walls or boulders. Grey nurse sharks rest in gutters, which is why so many NSW sites are called 'Shark Gutters'. Grey nurse shark sites →
Swim-through: A short tunnel, arch or gap in the reef that a diver can pass through with open water visible at the far end. Distinct from a cave, which has no visible exit and requires overhead training.
Cavern vs cave: A cavern is an overhead environment within the natural light zone and within about 40 m of the surface; a cave goes beyond it. Fish Rock is dived as a cavern-style swim-through by recreational divers; the Mount Gambier caves need cave certification. Cave & sinkhole dives →
Sinkhole (cenote): A water-filled collapse in limestone. The Mount Gambier region's sinkholes (Kilsby, the Shaft, Piccaninnie) are open shafts with clear groundwater; most require CDAA rating.
CDAA: The Cave Divers Association of Australia, which manages access to South Australian and other inland cave and sinkhole sites through membership and site ratings (Deep Cavern, Cave, Advanced Cave). Permits guide →
Ships' Graveyard: An official scuttling ground where obsolete vessels were sunk in deep water. Port Phillip Heads' graveyard holds the J-class submarines and more than 40 ships; Rottnest's graveyard holds wrecks from 30 to 200 m.
Scuttled wreck / artificial reef: A vessel deliberately sunk as a dive site, usually cleaned and cut with access holes. The ex-HMAS Brisbane, Canberra, Adelaide, Hobart, Swan, Perth and Tobruk are Australia's scuttled warships. Best wreck dives →
Penetration: Entering the interior of a wreck. 'Prepared' scuttled wrecks have cut openings and natural light throughout; unprepared wrecks and deep penetration require wreck training, a line and redundant gas.
Sponge garden: Temperate reef covered in sponges, ascidians, sea whips, gorgonians and bryozoans rather than coral. The signature habitat of southern Australian diving, from Nelson Bay to Port Phillip Heads to Bicheno.
Kelp forest: Reef dominated by large brown algae: Ecklonia (common kelp) throughout the south, and remnant giant kelp (Macrocystis) in Tasmania. Seadragons live along the kelp edges.
EAC (East Australian Current): The warm current that flows south down the east coast from the Coral Sea, strongest from November to May. It brings tropical species to Sydney and, when it meets cold water, sharp temperature changes and upwellings.
Leeuwin Current: The warm current that flows south along the WA coast, strongest in autumn and winter. It is why coral grows at the Abrolhos and Rottnest, and why WA's south coast is warmer than the equivalent latitude in the east.
Upwelling: Cold, nutrient-rich water rising to the surface, typically when offshore (north-easterly) winds push warm surface water away from the coast. Drops the temperature by several degrees overnight on the NSW south coast and in Victoria.
Swell period: The time in seconds between successive swell waves. Long-period swell (12+ s) carries more energy and wraps into sheltered sites; the number matters as much as the height when deciding whether a shore entry is on. How to read a swell forecast →
Sea breeze / Fremantle Doctor: The onshore wind that develops around midday in summer in every Australian capital as the land heats. Perth's is called the Fremantle Doctor. It is why summer shore dives happen at dawn.
Westerly / offshore wind: Wind blowing from the land to the sea, which flattens the surface and clears the water. Westerlies are the NSW shore-diver's friend; northerlies do the same for the Mornington Peninsula; easterlies for Perth.
Stinger season: November to May in tropical Queensland, the NT and northern WA, when box jellyfish and Irukandji are present inshore. Full-length lycra or neoprene is required on most boats and beaches. Wetsuit and stinger-suit guide →
Semi-dry: A thick (usually 7 mm) wetsuit with sealed neck, wrist and ankle cuffs and a dry zip, so it floods once and holds the water. The standard southern Australian suit between a wetsuit and a drysuit.
Marine park sanctuary (green) zone: A no-take zone within a marine park where fishing and collecting are banned but diving is allowed. Sanctuary zones consistently have the biggest fish and the best diving.
Aquatic reserve: The NSW term for a small coastal protected area, such as Cabbage Tree Bay at Manly, Bronte-Coogee and Long Reef, usually no-take and heavily dived.
Critical habitat: Legally gazetted areas around grey nurse shark aggregation sites in NSW and Queensland, with rules on anchoring, fishing gear and diver behaviour.
Dive traffic: This directory's estimate of how often a site is dived: from 'very popular (dived daily)' to 'remote/expedition only'. It is the best proxy for how reliably a visiting diver can get onto the site with an operator.
Data confidence: This directory's rating of how well documented a site is. High means several independent sources agree on location and depth; Low means a single mention or an approximate position. Low-confidence sites are flagged on their pages.
Approximate position: Coordinates in this directory marked approximate indicate the general area, not an exact entry point or mooring. They are for planning and should never be used for navigation.
Liveaboard: A vessel you live and dive from for several days. The only way to reach the Ribbon Reefs, the Coral Sea, the Rowley Shoals, the Far Northern reef and the Kimberley.
RFDS: The Royal Flying Doctor Service, which provides aeromedical evacuation from remote Australia. Divers injured at Ningaloo, the Kimberley, Cairns or the Coral Sea are flown by RFDS or state air ambulance to the nearest chamber. Dive safety and chambers →
DAN Asia-Pacific: The Divers Alert Network's regional organisation, which runs the 24-hour diving emergency hotline (1800 088 200) and evacuation insurance for Australian divers.