Meet the site
Fossil Cave, formerly known as the Green Waterhole and renamed on 4 May 1989, is a water-filled karst sinkhole in 30-million-year-old Oligocene coralline limestone beside the Princes Highway near Tantanoola. At the surface it is a modest depression about 20 x 10 m, but underwater it opens into a chamber roughly 70 m long and 30 m wide, reaching about 15 m deep. The CDAA describes it as a small pond leading to a broad chamber with dark silt at the bottom, and a small pool at the other end leading to a single small chamber.
Its fame is palaeontological. Since the mid-1960s divers and researchers have recovered Pleistocene subfossil material from depths up to 15 m, deposited mainly between 15,000 and 40,000 years ago. The species include the thylacine, the marsupial lion, giant kangaroos and two extinct birds – a giant coucal (Centropus colossus) and a large logrunner (Orthonyx hypsilophus). It is also the type locality for rare syncarid crustaceans otherwise known only from the Blue Lake. Fossils must of course be left undisturbed.
For divers the site is a Cave-category dive: Cave-rated divers may explore the chambers to 13 m but must not pass the signed restriction into the phreatic passage, which is for Advanced Cave divers only and forms part of the wider Tank Cave–Green Waterhole system (Wikipedia states Advanced Cave for all cave diving). The dark silt is the practical issue – it clouds instantly – so small teams and gentle technique are essential. It suits Cave-rated divers with an interest in natural history and good silt discipline.
Research this site before booking Stored site notes may be historical. These questions highlight gaps without turning old instructions into a current dive plan.
Fossil 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.
Topics flagged by the stored research
These are questions prompted by the existing notes, not a verified or complete hazard assessment.
- Overhead environments
- Ask whether the plan stays entirely in open water. A wreck or cave listing is not permission or training to enter.
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 Fossil 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 Fossil 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
Syncarid crustaceans (type locality), small freshwater invertebrates; Pleistocene megafauna subfossils in the sediments
Location
A water-filled karst sinkhole beside the Princes Highway near Tantanoola, 22 km north-west of Mount Gambier; 70 x 30 m underwater and 15 m deep, famous for Pleistocene megafauna fossils.
Facilities nearby
Roadside parking; no toilets. Tantanoola has a hotel; fills in Mount Gambier (22 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.auen.wikipedia.orgcavedivers.com.auRecord updated 26 Sept 2026. Source claims are being reviewed.