Meet the site
The Minmi Trench is a system of gullies on the northern side of the Botany Bay entrance, named for the coal that litters its sand and boulder gaps – almost certainly cargo from the collier SS Minmi, which was wrecked on Cape Banks on 13 May 1937, though some may be from the SS Woniora lost 2.5 km to the south-east. The reef top sits at 16–20 m and the main wall runs north-west to south-east, dropping to 22–23 m with sand extending to 26 m on the southern side. Between the wall and a line of large boulders lie three separate sections of trench, deeper towards the south, with numerous swim-throughs, overhangs and small caves concentrated south of the anchorage; to the north-east is a very large, low cave or overhang. The sponge life is outstanding – reds, blues, greens, yellows and whites – with sea squirts and gorgonians crowding the trench walls, and it is a productive site for macro. Fish and other life include eastern blue devilfish in the caves, red morwong, angelsharks and Port Jackson sharks on the sand, cuttlefish and octopus in the cracks, large schools of silver sweep and yellowtail over the reef, and black reef and mosaic leatherjackets. Because it sits in the bay entrance, tide governs the dive: on the ebb, particularly after rain, dirty water pours out over it, while on a high or incoming tide visibility of 12–20 m and more is normal. The site is large enough that even with a scooter McFadyen has covered only 500 m of it, and he considers it needs several dives. No charter boats currently visit, so it is a private-boat or St George Scuba Club dive, an easy 15 minutes from the Botany Bay ramps and a natural partner to Henry Head, Pink Floyd or the Cape Banks Caverns.
Research this site before booking Stored site notes may be historical. These questions highlight gaps without turning old instructions into a current dive plan.
Minmi Trench 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.
- 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.
- Lines and obstructions
- Discuss any known entanglement concerns and the suitability of the planned area.
- 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 Minmi Trench 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 Minmi Trench 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
Eastern blue devilfish, red morwong, angelshark, Port Jackson shark, cuttlefish, octopus, silver sweep, yellowtail, black reef and mosaic leatherjackets, sponges (many colours), sea squirts, gorgonians
Location
Series of trenches between large boulders and a NW–SE wall on the northern side of the Botany Bay entrance, between Henry Head and Cape Banks; reef top 16–20 m, wall to 22–23 m, sand to 26 m. Named for the coal from the SS Minmi scattered through it.
Facilities nearby
None (Botany Bay ramp facilities).
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.infomichaelmcfadyenscuba.infomichaelmcfadyenscuba.infoRecord updated 26 Sept 2026. Source claims are being reviewed.
