Three Rocks, or 3 Rocks, consists of three large bommies spread down a steep sandy slope that runs from about 2 m to 25 m. The slope is one of the drains of Wistari Reef, the large reef to the west of Heron, and water pours through it as the tide changes. When the current runs towards the old jetty, the site becomes one of Heron's best drift dives.

The moving water brings in pelagic fish that patrol the slope and the edge of the channel. The three bommies are covered in hard corals and host a variety of reef fish, and nudibranchs are common on the coral. Olive sea snakes are a feature: they come into the shallower water to feed before retreating to the deeper channel.

The usual plan is to descend to the deepest bommie, then drift from rock to rock, gradually ascending up the slope, which gives a natural multi-level profile. The sandy slope between the bommies is worth watching too, as rays and garden eels can be found there. Because of the depth and current, the site suits divers with some experience, ideally Advanced certification.

It is in the resort's top ten sites and is often chosen when the tide is running the right way. Divers who enjoy Three Rocks will also enjoy the Wistari Wall sites across the channel, which offer a deeper, steeper version of the same tidal environment. If the current is running the wrong way, guides may dive the bommies as a stationary dive from the deeper rock upward, returning along the slope, so the site can still be enjoyed away from the ideal tide.

Heron Island is 72 km north-east of Gladstone. Fly or drive to Gladstone, then take the Heron Islander ferry from the Gladstone Marina terminal (72 Bryan Jordan Drive; check-in from 7:45 am, departs 9:30 am on scheduled days, about 2 hours), or transfer by seaplane or helicopter. Dive gear is carried on the ferry in addition to baggage.

On the island, the dive centre sits beside the harbour; boats leave the jetty for three dives daily and most Heron Reef sites are 5-15 minutes away. Three Rocks is on the Wistari Channel side, about 5-10 minutes from the jetty.

Heron Reef sites are chosen on the day by wind and tide. The prevailing south-east trade winds (strongest April-September, often 15-25 knots) make the southern and south-eastern reef edge rough, so the sheltered northern and western sites are dived most. Northerly winds in spring and summer reverse this.

The tidal range is up to 3-4 m and currents run strongly around the reef edge and through Wistari Channel on springs; visibility is usually best on the incoming tide. Cyclone season is November-April; summer storms and plankton blooms can drop visibility to 10 m. Stingers are uncommon this far south but present in summer.

Three Rocks drains Wistari Reef, so it is a tidal site; it is best as a drift when the current runs towards the old jetty.

Enter up-current and descend the sandy slope to the deepest bommie at 20-25 m, then drift from rock to rock, ascending as you go. Watch the channel side for pelagics and sea snakes, and finish the drift in the shallows towards the old jetty with an SMB up.

Heron Island Resort Dive Centre is the only operator: three guided boat dives a day (about 9 am, 11 am and 3 pm) plus scheduled night dives, from the resort jetty; sites are rotated by tide and wind. Access requires a stay at Heron Island Resort (or the University of Queensland research station).