Meet the site
Cocklebiddy Cave is the most famous cave dive in Australia and one of the classic long cave penetrations of the world. The CDAA site description summarises it: an entrance chamber over 300 m long opens onto a 180 m lake, beyond which runs a single, straight tunnel more than six kilometres long, more than 90% underwater, following a fault due north. The first sump runs about 1 km to Rockfall Chamber, a large air chamber blocked by a rockpile about 25 m high; the second sump runs 2.5 km to Toad Hall; and the third about 1.8 km further.
Exploration began in the early 1970s. South Australian divers Hugh Morrison, Keith Dekkers and Phil Prust pushed 500 m in 1974 and reached the big chamber at the 1,000 m mark in 1976; the tunnel floor lies at about 13 m with the roof at 0-10 m. In 1983 Cocklebiddy became the world's longest known underwater cave after French and Australian expeditions pushed beyond Toad Hall, and later expeditions (including 1995 and 1997) extended the surveyed length beyond 6 km.
The water is gin-clear, often brackish, and the tunnel is enormous – divers describe elemental darkness in passages so big that lights fail to reach the walls, which can induce a form of agoraphobia. The dry chambers are huge boulder piles that must be crossed carrying equipment.
Access is tightly controlled. CDAA rates the cave Advanced Cave, and divers must apply in writing to DBCA at Esperance at least four weeks ahead with CDAA indemnity forms. It is extraordinarily remote – more than 1,100 km from Perth – with no rescue capability nearby, so every trip is a self-contained expedition. For qualified cave divers, the first sump alone is an unforgettable dive.
Research this site before booking Stored site notes may be historical. These questions highlight gaps without turning old instructions into a current dive plan.
Cocklebiddy Cave is recorded as Cave/Cavern in Nullarbor 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.
- Lines and obstructions
- Discuss any known entanglement concerns and the suitability of the planned area.
- Water movement
- Ask how swell and local exposure affect the proposed entry, exit and route.
- 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 Cocklebiddy 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 Cocklebiddy 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
None visible to most divers – cave-adapted invertebrates (stygofauna) and occasional bacterial growths; megafauna fossils recorded in Nullarbor caves
Location
One of the world's longest underwater cave passages: a single straight tunnel more than 6 km long, over 90% flooded, beneath the Nullarbor near Cocklebiddy Roadhouse.
Facilities nearby
None at the cave. Cocklebiddy Roadhouse nearby: fuel, meals, water, showers, accommodation.
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.aucavediving.net.audivernet.comnullarborroadhouse.com.auen.wikipedia.orgRecord updated 26 Sept 2026. Source claims are being reviewed.