Meet the site
Castle Rock is a single large bommie standing on the limestone and sand floor of Bass Strait south-west of Point Lonsdale, outside the Heads. The Scuba Doctor listing describes it as rising 'majestically out of a limestone and sandy bottom to around 12.0 metres on top', with 'many undercuts, splits and ledges' in its flanks and 'jagged rock turrets on top' that give it its name. It is roughly 200 m in circumference and the listing notes that divers can circle it once or twice in a dive – the whole site is a walk around a castle.
Because it stands in open water it carries a different community from the walls inside the Heads. The turrets and upper flanks are covered in yellow zoanthids and encrusting sponges, but the sand around the base is weedy seadragon country, and the listing records them here along with nudibranchs and sea stars. The fish list is long and typical of the Victorian open coast: southern blue devils in the undercuts, old wives, longsnout boarfish, dusky morwong, sixspine leatherjackets, scalyfin, zebrafish, bluethroat and senator wrasse and schools of sweep. Southern rock lobster are found under the ledges.
The depth range of 12–20 m and the ebb-tide preference make this one of the few Heads-area sites genuinely suited to Open Water divers, and operators use it as an 'outside' dive for mixed groups on calm days, often pairing it with Lonsdale Arches or Lonsdale Bommies on the same reef. The limiting factor is swell rather than current: it lies fully in Bass Strait and is unworkable in a south-westerly sea.
Research this site before booking Stored site notes may be historical. These questions highlight gaps without turning old instructions into a current dive plan.
Castle Rock is recorded as Pinnacle/Bommie in Port Phillip Heads. 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.
- Current and timing
- Ask how the operator assesses the current window for the actual route. Historical tide notes are not a departure instruction.
- Other water users
- Ask about vessel activity, exclusion areas and the agreed surface arrangements.
- 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 Castle 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 Castle 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
Weedy seadragon, southern blue devil, old wife, longsnout boarfish, dusky morwong, sixspine leatherjacket, scalyfin, zebrafish, bluethroat wrasse, senator wrasse, sweep, southern rock lobster, yellow zoanthids, nudibranchs, sea stars
Location
Large bommie outside Port Phillip Heads on the south-west side, about 1.6 km south-west of Point Lonsdale lighthouse in Bass Strait; 250 m from Deep Pinnacles.
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.auRecord updated 27 Sept 2026. Source claims are being reviewed.
