SS Yongala

The Yongala vanished in a cyclone in March 1911 with all 122 people aboard, and was not confirmed found until 1958. What remains is the most crowded piece of seabed most divers will ever hover over: the only hard structure for miles of open sand, it concentrates life at absurd density. Queensland grouper the size of the tenders loiter under the hull, marble rays carpet the sand, eagle rays and turtles commute along the deck line, sea snakes hunt through the soft-coral shag that coats every surface, and bull sharks patrol the green edge of visibility. Entry to the wreck is prohibited by law, and it is dived as a grave as much as a site.

The moment you come for: Extraordinary fish density, giant Queensland grouper, marble rays, a century-old story held with respect

Topography: Open sand at about 30 m with the 109 m steamer lying on its starboard side

Current: Current is the site's defining variable, from gentle to hand-over-hand; briefings and line discipline matter.

Entry: Reached by a short, often bumpy crossing from Alva Beach near Ayr, or longer runs from Townsville and Magnetic Island; descents and ascents use the mooring lines only.

Hazards: Current, exposure of an open-water site, depth for the full circuit, and boat traffic at the moorings.

Permits & rules: Dives run through operators permitted under Australian underwater cultural heritage protections.

Conservation: A protected historic wreck and the grave of 122 people: no penetration, no touching, no artifacts, moorings only.

Nitrox: Worth it here — profiles sit in the range where enriched air meaningfully extends no-stop time (with the training to use it).