Sir John Young Banks is the most serious dive in this region – an offshore reef system 16 km out from Crookhaven Heads that rises from depths of more than 70 m to a plateau as shallow as 16 m. The main dive is on the 33 m reef, which runs roughly north–south and drops to a narrow shelf at 42 m before a second wall falls to 50 m. Other marks give an 18 m reef and a 40 m+ reef, and a northern reef is also charted.

The banks are a magnet for pelagic life. McFadyen lists tuna, yellowtail kingfish, hammerhead sharks, oceanic whitetips, and grey and bronze whalers, alongside cuttlefish, leatherjackets and swirling bait. The fixed life is spectacular: sea whips, sponges and sea squirts cover the walls, and nudibranchs and sea stars are abundant. He describes the colours as unlike almost any other dive, a result of the clear oceanic water and the absence of kelp at depth.

This is not a site for casual visits. The banks are usually swept by currents from the north, often strong enough to make anchoring and descending difficult, and the presence of large sharks, the depth, the distance from shore and the Crookhaven bar all add risk. Divers need a capable boat with a skipper who stays aboard, excellent sea conditions, and experience in deep open-ocean diving; most visits are by technical divers using trimix or nitrox with decompression gases. For those who can meet those conditions it is one of the most spectacular offshore dives on the NSW coast, and it is rarely dived, so the reef remains in pristine condition.

Launch at the Crookhaven Heads boat ramp at the mouth of the Shoalhaven River (one of the region's largest ramps; trailer parking and toilets), about 2.5 hours south of Sydney. Cross the Crookhaven bar with care and run 18 km east-south-east to the banks – at least 30–35 minutes, sometimes under 25 in flat seas. GPS is essential: marks (WGS84) are 18 m reef 34° 56.922' S 150° 55.737' E; 33 m reef 34° 56.939' S 150° 55.770' E; 40 m+ reef 34° 56.955' S 150° 55.787' E.

Anchor on the 33 m reef.

A fully exposed offshore site: it needs a long spell of calm weather with swell under about 1 m and light winds, both for the 18 km run and for the Crookhaven bar, which breaks dangerously in easterly swell and on an ebb tide. Currents from the north are the rule rather than the exception – when the East Australian Current is running they can be too strong to dive. Visibility is typically excellent (15–30 m) in oceanic water.

Plan to be back across the bar before afternoon north-easterly sea breezes build.

Anchor on the 33 m reef, descend and look over the edge at the narrow shelf at 42 m and the wall dropping to 50 m. Technical divers drop the wall; recreational divers stay on the 33 m reef. In current, drift along the wall on a float line with the boat following.

Run a planned decompression ascent up the anchor line or on a DSMB.

Plan as a technical dive: EAN28–32 for the 33 m reef or trimix (e.g. 21/35) for the 50 m wall, with EAN50/oxygen for decompression; drift decompression on a DSMB if current pulls the anchor. Full redundancy and a surface support boat essential.

No regular operator – private boats and technical diving groups on calm days only; occasionally visited by Jervis Bay or Sydney technical charters.