Half Tide Rock is an outcrop off Great Keppel Island's northern coast that breaks the surface around mid tide, giving it its name. Underwater it forms a small rocky reef reaching about 12 m, draped in soft corals and dotted with anemones and their resident fish. The site's attraction is the density of colour on a compact structure.

Soft corals grow thickly on the rock faces, and the anemones hold clownfish and anemone shrimp. Reef fish congregate around the rock, and olive sea snakes are frequent visitors, foraging in the cracks. The dive usually consists of circling the rock at a couple of depths, which makes navigation simple, but divers should be aware that the shallow top attracts surge when swell is running and that tidal flow along the north coast can pick up.

It is best dived close to slack water in south-easterly conditions. Half Tide Rock suits Open Water divers comfortable with a bit of current and makes a good macro and soft-coral photography dive. It is less often visited than the southern and western sites, so it tends to feel quiet.

It should not be confused with Halfway Island, south of Great Keppel, which older listings sometimes group with it. The rock is a navigation hazard for boats at mid to high tide, so dive boats approach carefully and anchor on sand some distance away. Because published information on this site is limited, divers should rely on the operator's briefing for current conditions, likely currents and the best side of the rock on the day.

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. Half Tide Rock lies off the northern coast of Great Keppel, about 10-15 minutes by dive boat from Fisherman's Beach or 35 minutes by private boat from Rosslyn Bay.

The rock partly uncovers at low tide; boats anchor on sand nearby.

Keppel Bay is exposed to the prevailing south-east trades (strongest April-September) and to summer northerlies. The northern coast of Great Keppel is sheltered in south-easterlies but exposed to northerlies. As the name suggests, the rock is half-exposed at mid tide and surge breaks over it when swell is running.

Tidal currents flow along the north coast on springs; dive near slack. Visibility 5-12 m.

Descend to the base of the rock at 10-12 m and circle it with the current behind you, inspecting the soft corals and anemones, then ascend to 5 m and do a second lap before the safety stop in the lee of the rock.

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. Dived occasionally.