Mount Gambier · Australia · Freshwater · Cave & cavern
Fossil Cave
A roadside sinkhole in 30-million-year-old limestone
Area photo: Mark Whatmough · CC BY 2.0
Fossil Cave, site 5L81, is a flooded karst sinkhole near Tantanoola on the Limestone Coast, formed in limestone around 30 million years old. It lies about 22 kilometres north-west of Mount Gambier and only metres off the Princes Highway, and it drops to roughly 15 metres below the water surface.
Where it is and how deep
37.7319° S, 140.5311° EPublished position for this site.
The dive
The entry is a flooded karst sinkhole in the Limestone Coast plain, cut into limestone that formed about 30 million years ago. From the surface pool the dive works down into the flooded rock, reaching approximately 15 metres below the water surface. It is shallow by the standards of the district's deeper shafts, but the depth number is not what sets the grade here.
What does set it is the overhead. The Cave Divers Association of Australia restricts cave diving at Fossil Cave to holders of its Advanced Cave grade, and the site's own hazard profile is silting plus true overhead conditions with no direct ascent to the surface. Plan it as a cave dive with continuous line, gas reserves and a team trained for zero-visibility exits rather than as a 15-metre sinkhole bimble.
Marine life and season
The sources we used don't single out particular species here.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Good | Good | Good | Good | Prime | Prime | Prime | Prime | Fair | Fair | Fair | Good |
Season follows Mount Gambier: Every site is spring- or aquifer-fed, so temperature holds steady all year; the one fixed closure is Ewens Ponds from 1 September to 30 November, and winter is reported as Kilsby's clearest water.
Know before you go
- Silt: the fine sediment here goes up easily and takes the visibility with it, which is why exits are planned on line and by touch.
- Overhead conditions with no direct access to the surface — the reason the CDAA holds cave diving here at Advanced Cave grade.
Questions divers ask
Where is Fossil Cave?+
In the Limestone Coast region of South Australia near Tantanoola, about 22 kilometres north-west of Mount Gambier and only metres from the Princes Highway.
Do I need a cave certification for Fossil Cave?+
Yes. Access for cave diving is limited to holders of the Cave Divers Association of Australia's Advanced Cave grade, because of the silting and overhead conditions.
Sources
- Fossil Cave — Wikipedia
- Cave Dive Sites by Region — Cave Divers Association of Australia
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