Meet the site
Marys Reef is a relatively recent find: St George Scuba Club member Phil Short discovered it around 2012, and it has become one of the club's favourite Royal National Park sites. It lies south of Barrens Hut and The Balcony. The reef has a flat top at 16–17 m at the mark. To the south the depth increases to just over 20 m where the sand begins, and the wall there is a sheer drop of over three metres. Towards the north-east of the reef the sand reaches about 24 m. Along the wall are multiple overhangs – the main one is at about 20 m – caves, boulders and gutters, and shallower gullies lead back across the reef. The wall is lined with sea tulips and sponges, with a few attractive gorgonians. Fish life includes one-spot pullers, eastern blue devilfish, leatherjackets, seapike and large bullrays, and Port Jackson sharks are common from August to October. Nudibranchs such as the splendid chromodoris add colour. Bottom time is about 30–35 minutes on air or 40–45 minutes on 32% nitrox. Like every site south of Botany Bay, there is no charter boat that dives here, so it requires a private boat or club membership. Anchoring depends on the wind – on sand in a southerly, otherwise on the reef top with plenty of line. It suits Advanced divers looking for a varied reef with good invertebrate life, and it combines well with a shallower second dive at The Balcony or Marley Point on the same calm-day trip down the national park coast.
Research this site before booking Stored site notes may be historical. These questions highlight gaps without turning old instructions into a current dive plan.
Marys Reef (Royal National Park) is recorded as Reef in Sydney South & Botany Bay. 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.
- 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 Marys Reef (Royal National Park) 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 Marys Reef (Royal National Park) 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
Sea tulips, sponges, gorgonians, one-spot puller, eastern blue devilfish, leatherjackets, seapike, bullray, Port Jackson shark (Aug–Oct), splendid chromodoris and other nudibranchs
Location
Flat-topped reef with a sheer 3 m+ wall, overhangs, caves and boulders south of The Balcony off Royal National Park; top 16–17 m, sand 20–24 m.
Facilities nearby
Departure only: Port Hacking ramps – Tonkin Park/Gunnamatta Bay (Cronulla), Lilli Pilli, Bundeena – with parking and toilets; air/nitrox at Pro Dive Cronulla and Abyss (Ramsgate).
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
michaelmcfadyenscuba.infoRecord updated 26 Sept 2026. Source claims are being reviewed.
