Hannah Rock is the deeper of the two reefs off Great Keppel Island's southern coast, reaching about 30 m. It is a dive for experienced divers that trades the colourful shallow coral of the western bays for a deeper, darker world of sea whips and black coral trees. The lower reef is dominated by whips and black coral trees, some of them large, which grow in the moderate current.

Among their branches live small gobies, shrimps and whip crabs, and larger fish congregate around the structure. The site is noted for large pelagic fish, such as trevally and mackerel, which cruise past the edge of the reef, and for the chance of rays and reef sharks. Because of its depth and exposure, Hannah Rock is rarely dived, which gives it a pristine feel but also means current information is limited: rely on the skipper's local knowledge and choose a calm day.

Visibility is typically moderate for the inner bay, and light levels at 20-30 m can be low, so a torch is useful for bringing out the colour of the whips and corals. Hannah Rock suits Advanced divers who are comfortable with depth and moderate current. Divers who want the same type of habitat with less depth can dive nearby Bald Rock, which is shallower and more often visited.

Pair the two on a calm day for an interesting contrast between the shallow plate-coral reef and the deep whip garden.

Drive 40 km (about 40 minutes) from Rockhampton to Yeppoon, then 7 km south along the Scenic Highway to Keppel Bay Marina at Rosslyn Bay Harbour, where there is free and paid parking. Freedom Fast Cats and Keppel Konnections ferries run to Great Keppel Island (Fisherman's Beach) in about 30 minutes; Keppel Dive & Water Sports picks up certified divers from the island. Hannah Rock lies off the southern coast of Great Keppel, about 15-20 minutes by dive boat from Fisherman's Beach or 40 minutes by private boat from Rosslyn Bay.

Boats anchor on sand nearby in calm weather.

Keppel Bay is exposed to the prevailing south-east trades (strongest April-September) and to summer northerlies. Hannah Rock faces the prevailing south-easterlies and is dived only in calm spells or light northerlies with minimal swell. Tidal currents are stronger at depth on springs; neap tides and slack water are preferred.

Visibility is typically 8-15 m, best July-October, and deteriorates after rain.

Descend the anchor line to the top of the reef, then follow the slope down to the black coral and whip zone at 20-25 m. Keep an eye on the blue for pelagics, turn at your planned no-decompression limit or half air, and ascend slowly along the reef to finish at 5 m.

Keppel Dive & Water Sports (PADI 5 Star, based on the Spit at Great Keppel Island next to Great Keppel Island Hideaway) runs guided boat dives to the Keppel sites most days, weather permitting, plus courses and Discover Scuba; site choice is made on the day according to wind. Private boats from Rosslyn Bay also dive here. Hannah Rock is dived only occasionally, in calm conditions, for experienced divers.