Meet the site
Bum Rock is the Glennie Group's landmark: a massive smooth granite boulder on the western side of Dannevig Island split by a large central crack that, as Scuba Doctor puts it, looks just like its name. The crack runs from above the waterline about 10 m down into the rock, and the boulder stands on a boulder-covered bottom at 30 m or more, so the dive is a descent through or beside the cleft to the base and a circuit of the giant block and its neighbours. It is a wall dive in effect – the sides of the boulder are sheer for 20 m – and, being on the exposed western face of the island in the path of every Bass Strait swell, it carries growth to match: a band of bull kelp in the surge zone, then sponge, zoanthid, gorgonian and sea-whip cover thickening with depth, jewel anemones and bryozoans in the crack and under the overhangs, and crayfish deep in the base. Fish schools – butterfly perch, sweep, bullseyes – hang in the eddies on the lee side of the rock, boarfish and morwong work the ledges, and seals from the Glennie haul-outs often follow divers around the boulder. The hazard is surge, which Scuba Doctor describes as very strong; the crack concentrates it and the shallow part of the dive can be a washing machine on days when the rest of the island is diveable. Bum Rock is therefore a rare-day dive even by Prom standards, attempted when a club or private boat at Tidal River finds an easterly wind and a flat western swell, and it is prized as much for the photograph of the boulder from the boat as for the dive. For an Advanced diver in the right conditions it is a memorable, almost sculptural piece of granite topography with the clear water and colour of the outer Glennies.
Research this site before booking Stored site notes may be historical. These questions highlight gaps without turning old instructions into a current dive plan.
Bum Rock is recorded as Wall in Wilsons Promontory. The listed access is boat. 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.
- Other water users
- Ask about vessel activity, exclusion areas and the agreed surface arrangements.
- Planned depth
- Confirm the intended route and training requirements; the recorded maximum is not a target.
- Water movement
- Ask how swell and local exposure affect the proposed entry, exit and route.
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 Bum Rock suitable for my certification?
The record lists Advanced Open Water. 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 Bum Rock 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
Bull kelp, sponges, zoanthids, gorgonians, sea whips, jewel anemones, bryozoans, southern rock lobster, butterfly perch, sweep, bullseyes, boarfish, morwong, Australian fur seals
Location
Massive split granite boulder on the western side of Dannevig Island in the Glennie Group, 620 m south-south-west of the island's north-east tip.
Facilities nearby
Departure from Tidal River beach ramp, Port Welshpool or Sandy Point; No air fills at Tidal River or Port Welshpool; the nearest compressor is roughly 100 km away (Melbourne's south-east or Inverloch/Leongatha area by arrangement) – bring all cylinders or a portable compressor
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
scubadoctor.com.auscubadoctor.com.auscubadoctor.com.auRecord updated 26 Sept 2026. Source claims are being reviewed.