Whale Bones takes its name from the whalers of the 1830s-1850s, who are said to have dumped whale bones here; none are visible today. What remains is one of the most intricate reef structures on the Fleurieu: a big system of limestone caves, undercuts, swim-throughs and reef that the Federation calls a virtual honeycomb of caves and passages. The top of the reef lies in only 2-3 m, and it is pocked with holes that lead down into the cave system beneath.

On the seaward side there is a small drop-off, and the undercuts and cave mouths are found along this edge in 5-10 m. Thick kelp covers the reef top, and inside the caves the walls are encrusted with sponges and other invertebrates. The Marine Life Network lists seadragons, blue devils, seals, juvenile blue groper, drummer, perch, harlequin fish and scalyfins.

Harlequin fish, a cold-water reef species, are a particular treat. Because the site is off the beaten track compared with the Bluff, fish are relatively relaxed. The Whale Bones is best for divers comfortable in overhead environments who keep to short swim-throughs with visible exits; true cave penetration requires cave training.

The shallow reef means surge can be strong, and the site cannot be dived in high swell. Access from shore is tiring because of the long wade through knee-deep water, so many divers prefer to come by boat. On a calm northerly day, it is one of Victor Harbor's most interesting dives.

A torch is essential for looking into the undercuts, where crayfish and cave-dwelling fish shelter out of the light.

In Victor Harbor, head along the Esplanade toward Encounter Bay; the Federation directs divers to turn at the hospital toward Encounter Bay, with the reef in front and to the right of the road junction. Park on the esplanade. A white marker identifies the reef top.

From shore, walk and wade across more than 100 m of knee-deep water before swimming out – tiring with scuba gear – or launch a small boat at the Bluff ramp and run a few minutes east.

Encounter Bay faces south into the Southern Ocean swell that wraps around Kangaroo Island and Cape Jervis, so Victor Harbor sites are the reverse of the gulf coast: they need northerly (offshore) winds. The best days follow several days of northerlies with low southerly swell, when visibility improves and the swell is blown back; any southerly or south-westerly swell over about 1 m, or strong southerly winds, makes most sites undiveable and stirs up particles. Summer and autumn bring the most northerly days, but good windows also occur in winter ahead of cold fronts.

Tidal currents strengthen around the headlands and islands during large tidal movements. Southern right whales visit Encounter Bay from about June to October – keep legal approach distances. Water is a little cooler than in the gulf.

The Whale Bones reef is shallow and cannot be dived in high swell; surge through the caves is a real hazard.

Descend at the white marker onto the reef top at 2-3 m, then drop down the seaward side to 6-10 m and explore the undercuts and cave entrances along the edge. Only enter short swim-throughs where the exit is visible, and return over the reef top.

Short swim-throughs only for recreational divers; any real penetration requires cave/cavern training, lights and a guideline.

No regular operator; visited by club dives and independent divers; occasionally included on Victor Harbor trips by Adelaide shops.