Castle Rock is a classic reef / bommie dive located just outside Port Phillip Heads on the Point Lonsdale (south-west) side of the entrance to Port Phillip Bay, near Melbourne, Victoria. It’s one of the region’s most popular boat dives for Open Water-certified divers, thanks to its manageable depth, distinctive structure and marine life.

Dive Profile

  • Type: Reef / bommie dive

  • Access: Boat dive

  • Latitude: 38° 17.887′ S  Longitude: 144° 35.863′ E

  • Depth: Rises from about 18–20 m on the sandy bottom to the top around ~12 m below the surface

  • Conditions: Generally easy navigation with minimal current on most days, making it suitable for newer Open Water divers

Site Features
Castle Rock stands out as a prominent outcrop — roughly 200 m in circumference — rising up from the sandy sea floor to form a compact, castle-like feature underwater. The rock is pitted with undercuts, ledges and swim-throughs, giving divers plenty of structure to explore. You can easily circle the formation on a single dive, with plenty of hiding spots and overhangs to investigate.

Marine Life & Highlights
This dive is noted for its temperate marine life typical of southern Australian waters. Around the bommie you may spot:

  • Weedy seadragons and other small critters grazing on the rock surfaces

  • Port Jackson sharks in the vicinity

  • Southern blue devils and other reef fish around cracks and crevices

  • Occasional crayfish tucked under ledges and macro fauna scattered across the rock

Why Divers Like It
Castle Rock’s stable depth range, recognisable underwater topography and variety of life make it a great choice for both training dives and enjoyable recreational dives. Its well-defined structure and relatively mild conditions offer a comfortable environment for divers building confidence in open-water marine conditions.

Note: As with all dives around Port Phillip Heads, planning around tidal slack and sea conditions is important, and most dives are done via boat with experienced local operators

Top