Meet the site
Tank Cave is the most extensive underwater cave in South Australia and the benchmark Advanced Cave site in the country. It lies near Tantanoola, is owned outright by the Cave Divers Association of Australia, and its entrance is underground: a short ladder leads down to a small surface lake, and from there the system spreads out into a maze of more than 7 km of diveable passage, around 10 km including the connected Green Waterhole (Fossil Cave) system. That makes it the second-longest underwater cave in Australia after the Nullarbor systems.
What makes Tank special is its character rather than its depth. Most of the cave lies shallower than 15 m, with typical depths around 10 m, so dives can last two hours or more with modest decompression. The passages are a labyrinth of low bedding planes, wider tunnels, chambers and connections, with white and brown limestone, fine clay banks and silt floors. Fixed lines run through most main passages, but side passages need jumps, and the sheer number of junctions is the challenge – navigation, line protocol and gas management matter more here than anywhere else in the region. Divers continue to find new passages and connections decades after exploration began.
Tank has seen deaths: two divers died in 2011, including explorer Agnes Milowka, and an experienced Victorian cave diver died in November 2025, after which the CDAA ran an internal investigation. Access is therefore controlled by an Access Officer roster and a staged familiarisation schedule. It suits CDAA Advanced Cave divers who want long, shallow, navigation-heavy cave dives – sidemount and rebreather divers especially.
Research this site before booking Stored site notes may be historical. These questions highlight gaps without turning old instructions into a current dive plan.
Tank Cave is recorded as Cave/Cavern in Mount Gambier Sinkholes & Caves. The listed access is shore. Confirm the actual meeting point, route and permission to visit; a map pin does not establish any of these.
Historical access notes exist for this record, but have not been independently verified for current use. Request current directions from the operator or site manager rather than following an old entry description.
Questions, answered
Is Tank Cave suitable for my certification?
The record lists Cave/Cavern certification. That does not establish suitability for every route or day. Share your training, recent experience and equipment needs with the operator and ask about the specific proposed dive.
Can I book Tank Cave through YouDive?
YouDive is an independent research directory. Contact an operator directly to confirm whether it currently runs the trip, the inclusions and the booking terms.
What you might see
Minimal – occasional cave-adapted crustaceans (syncarids) and small invertebrates
Location
Owned by the CDAA, an underground-entrance maze cave near Tantanoola about 25 km north-west of Mount Gambier, with more than 7 km of lined passage (about 10 km with the connected Green Waterhole system).
Facilities nearby
CDAA-owned site with parking at the entrance; no public facilities. Fills in Mount Gambier (25 km).
Before you make plans
Conditions, access and operator schedules can change. This is a location guide, not a dive plan. Ask a local operator about current conditions and suitability for your training and experience.
Sources & further reading
cavedivers.com.audivernet.comdivedb.netscuba.comen.wikipedia.orgRecord updated 26 Sept 2026. Source claims are being reviewed.