North Bommie is a single, giant mushroom-shaped coral head on the northern edge of Heron Reef, about 100 m north of Blue Pools. It is relatively shallow and an easy dive, but it packs in a great deal of life, because the bommie is a major cleaning station for this part of the reef. The bommie is surrounded by clouds of glassfish and cardinalfish, which in turn attract predators: coral trout, coral cod, butterfly cod and barramundi cod hunt through the schools throughout the day.

Large manta rays and sea turtles come in as regular cleaning clients, often hovering above the bommie while cleaner wrasse work over them. Guides have long pointed out resident leaf scorpionfish living on the bommie, colour morphs that the dive team have named over the years, which reward those who look closely. The overhanging 'mushroom' cap creates shaded undercuts where the glassfish shelter and where torchlight brings out the colours of sponges and soft corals.

Because it is a single structure, navigation is simple: circle the bommie, then wait at the cleaning station. The site suits all levels and is particularly good for photographers, who can capture both the swirling baitfish and the mantas when they arrive. North Bommie is in the resort's top ten sites and is often paired with Blue Pools on the same trip.

It is worth visiting more than once, since manta and turtle visits vary with season and tide. Give the cleaning station space: mantas and turtles abandon it quickly if divers crowd the top of the bommie, so settle on sand to one side and let the animals come to you.

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. North Bommie is about 100 m north of Blue Pools, 5-10 minutes from the jetty, and is dived from a mooring.

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.

North Bommie is on the sheltered northern side; strong northerlies or large north-east swell make it less comfortable.

Descend the mooring to the base of the bommie, circle it slowly at 12-16 m, and then settle at a distance from the cleaning station and wait for mantas and turtles. Look for the resident leaf scorpionfish, then spiral up to the top of the bommie for the safety stop.

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).