Cave system
Green Waterhole - Tank Cave system
The CDAA booking page gives 'over 10 kilometres' of intersecting passage; the older CDAA site directory entry says over 7 km, and a 1994 CDAA article reprint put mapped passage at close to 6 km. The figures reflect continuing exploration.
A maze of intersecting flooded passages near Tantanoola with more than 10 km of passage according to the CDAA, which owns the main Tank Cave entrance. A 2018 dive connected it to Green Waterhole (Fossil Cave).
The Green Waterhole - Tank Cave system lies near Tantanoola, north-west of Mount Gambier. Its main entrance, Tank Cave, takes its name from a water tank that once stood over the opening; divers climb down a short ladder to a small pool that leads into a maze of interconnected phreatic tunnels (passages dissolved while completely full of water). A guideline (a fixed navigation line) runs through much of the cave, and many side passages require divers to bridge from one line to another.
The CDAA describes the system as the longest underwater cave in South Australia and the second-longest in Australia. Diving is restricted to CDAA Advanced Cave members, the cave is used for final assessment dives on the Advanced Cave course, and every diving day needs a CDAA site access officer. The second natural entrance, Green Waterhole (now officially Fossil Cave), sits on state land and is booked through the parks service.
The association bought the land over the Tank Cave entrance in 2010. Exploration in recent years has added several kilometres of passage, including the 2018 connection to Green Waterhole and fossil deposits at the western end, an area the CDAA says has received provisional State Heritage listing as the Green Waterhole - Tank Cave Fossil Complex.
Why it matters
Long-term focus of CDAA training, exploration, survey and conservation work. The CDAA reports fossil deposits at the western end of the system and a provisional State Heritage listing of the Green Waterhole - Tank Cave Fossil Complex (date of listing not given on the page).
Survey and exploration history
| 1994 | CDAA divers extended the mapped cave by several hundred metres, bringing mapped passage to close to six kilometres. [4] |
| 2010 | The CDAA bought the land over the Tank Cave entrance. [1] |
| 2018 | Divers connected Tank Cave with Green Waterhole (Fossil Cave). [1] |
Entrances and dive sites
Two known natural entrances: Tank Cave (on CDAA-owned land, CDAA-managed) and Green Waterhole / Fossil Cave (state land, booked through the parks service).
For orientation, not navigation. Hollow dots are approximate.
Every fact on this page, with its source (10)
| Fact | Status | Source |
|---|---|---|
| Tank Cave has over 10 kilometres of intersecting phreatic passages.CDAA booking page (undated, viewed 2026-10-14): over 10 km. CDAA site directory entry: over 7 km. 1994 article: close to 6 km mapped. Older figures predate later exploration; no dated survey total was found. | Sources conflict | [1] [2] [4] |
| The CDAA calls the system the longest underwater cave in South Australia and the second-longest in Australia.Self-description by the managing association. | Reported | [1] |
| Tank Cave was connected to Green Waterhole in 2018. | Verified | [1] |
| The CDAA purchased the land over the primary entrance in 2010. | Verified | [1] |
| Access to the Green Waterhole - Tank Cave system is restricted to CDAA Advanced Cave divers; the Tank Cave entrance is managed by the CDAA and Green Waterhole by the Department for Environment and Water.The DEW booking page separately allows CDAA Cave-rated divers into Fossil Cave (Green Waterhole) above 13 m in the phreatic passage. | Verified | [1] |
| A qualified Tank Cave site access officer is required for each diving day and a familiarisation schedule must be completed. | Verified | [1] [2] |
| Fossil Cave requires a CDAA Cave qualification, and divers must not go beyond 13 metres into the phreatic passage unless qualified to Advanced Cave level. | Verified | [3] |
| In 1994 CDAA divers added more than 700 m and about 400 m of new passage on separate dives, and the article put mapped passage at close to six kilometres.Historical figure from 1994. | May be out of date | [4] |
| Area coordinates are the mapped centre of the Tantanoola locality, not an entrance.Entrance coordinates deliberately withheld; the CDAA directory places the Fossil Cave entrance at Tantanoola (s5). | Verified | [6] |
| Area coordinates are the mapped centre of the Tantanoola locality, not an entrance.Entrance coordinates deliberately withheld; the CDAA directory places the Fossil Cave entrance at Tantanoola (s5). | Verified | [6] |
Verified: stated by an official or primary source we opened. Reported: from a secondary source only. Sources conflict: the note gives both versions. May be out of date: the newest source we found is old.
Written in our own words from the sources above. Report a correction