Hump One is the first of a series of deep reefs – the Humps – that sit off the very end of Bass Point Reserve. It is a compact, pear-shaped reef about 50 m long and 30 m wide, pointed at its southern end, with its top at about 27 m and surrounding sand just over 35 m. Across the broader hump field the sand lies between about 24 and 35 m.

Because it is small, a full circuit can be completed in about seven minutes at a slow pace, which suits the short no-decompression times on air at this depth. The attraction is the density of fixed life: sponges, sea whips and sea squirts cover the reef, gorgonians are especially abundant on the eastern and southern sides, where the walls are steepest, and sea stars and many species of nudibranchs dot the rock in large numbers. Fish include leatherjackets, yellowtail, sweep, striped seapike and boarfish, with Port Jackson sharks resting on the sand in season and kingfish cruising in the blue.

The site is marked by McFadyen as a deep dive only for the experienced. Anchoring is awkward because the rocks lie at right angles, which can lead to anchors dragging or jamming; many groups prefer a shot line. The Humps are more exposed than the inshore Bass Point reefs, and current is more common. For experienced divers with good gas planning – ideally on nitrox – it offers a rare chance to see pristine deep temperate reef growth only 10 minutes from a boat ramp, and the neighbouring Hump Wall gives a second option at similar depth.

Launch from the Shellharbour Marina boat ramp (Shellharbour Village; trailer parking and toilets), about 105 km and 1.5 hours south of central Sydney. Head east out of the harbour and around Bass Point; run almost due east about 3.5 km (under 10 minutes) to 34° 35.126' S 150° 54.769' E off the end of Bass Point Reserve. Use the sounder to find the reef rising from 35 m to 27 m; the rocks lie at right angles and give poor anchor holding, so use a shot line or a grapnel with plenty of scope.

Bass Point juts well out to sea south of Shellharbour, so its outer reefs take swell from the north-east through to the south. Boat dives here want a swell under about 1.5 m and moderate winds; in a south-easterly the outer sites become rough very quickly, and the short run from Shellharbour Marina means operators can come back in if conditions build. Westerly winds in late autumn and winter give the best flat seas and clearest water, often 15–20 m.

Visibility drops after big seas stir the sand and after heavy rain. The Humps are more exposed than the inshore reefs and current is more likely; abort if the anchor line is streaming.

Descend the shot to the reef top at 27 m and do a slow circuit of the hump – about seven minutes – concentrating on the eastern and southern walls where the gorgonians are best. Return to the line with a margin on no-deco limits and ascend with a slow safety stop.

Nitrox (EAN28–30) or a planned light-deco profile; carry a DSMB. Consider a shot line rather than anchoring.

Occasional private and club boats and experienced groups with Shellharbour Scuba and Photography Centre; not a regular charter site.