Meet the site
Castle Rock is an unusual patch reef standing off the main body of Agincourt Reef No. 1, and it is one of the sites on the Agincourt roster where larger animals most reliably congregate. Both Silverseries and Poseidon describe it the same way: a 24 m exposed wall on one side and a spectacular garden reef on the lee side. That split personality is what makes the dive. On the exposed face the rock drops fairly steeply from about 5 m to sand at 24 m. The wall is cut with ledges and overhangs where moray eels and coral trout sit, and its position means current regularly pushes across it, bringing in schooling fish and the predators that follow them. Reef sharks patrol the base, groper (Queensland and estuary cod) hang under the overhangs, and oceanic sweetlips and oceanic trout move along the face. Anthias swarm over every outcrop in the flow. Swing round to the lee side and the character changes completely: a sheltered, shallower garden of hard corals, plate and staghorn, with anemones, clownfish and reef fish in calm water. This is where you finish the dive and do your safety stop, and it is where snorkellers get the best of the site. The site suits open water divers who are comfortable holding depth beside a wall, and it is a favourite of more experienced divers for the chance of big fish. Current can run on the exposed side during spring tides, so guides may run it as a gentle drift or keep the group on the sheltered side if conditions are lively. Visibility often reaches the high 20s and occasionally 35 m, and the contrast between the dark wall and the bright shallow garden makes for good wide-angle photography. As with all Agincourt sites it lies within a Great Barrier Reef Marine Park zone where fishing and collecting are prohibited, which helps explain the size of the cod and trout. If the skipper offers Castle Rock, take it – it packs a lot of variety into one 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.
Castle Rock (Agincourt Reef 1) is recorded as Pinnacle/Bommie in Port Douglas. The listed access is boat (day trip). 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.
- 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 Castle Rock (Agincourt Reef 1) 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 (Agincourt Reef 1) 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
Grey and whitetip reef sharks, Queensland groper, oceanic sweetlips, coral trout, moray eels, anthias, fusiliers, clownfish, plate and staghorn corals
Location
An isolated patch reef off Agincourt Reef No. 1 with an exposed 24 m wall on its seaward face and a garden reef on the lee side.
Facilities nearby
Departs Crystalbrook Superyacht Marina, Wharf Street, Port Douglas – car parking, toilets, cafes and restaurants at the marina; dive shops in town for gear hire and air
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
silverseries.com.auposeidon-cruises.com.auRecord updated 27 Sept 2026. Source claims are being reviewed.