Gordon's Mooring is a relaxed, intricate dive among a cluster of smaller bommies rather than a single wall or pinnacle. The coral heads rise from sand at up to about 22 m, and many are close enough together to form short swim-throughs, arches and overhangs; others are separate towers you can circle in a few minutes. The coral is dominated by brain and plate corals, and one of the site's signatures is a garden of giant clams in the shallows, with dozens of mantles in blue, green and brown lining the sand and rubble.

Because the bommies break up the current, the site is usually calm and easy to navigate, and it rewards divers who slow down. Clownfish are common in anemones on the bommie tops, yellowtail fusiliers and other schooling fish stream past, and great barracuda often hang motionless off the edge of the field. Reef sharks patrol the sand channels.

Gordon's is one of the better Cairns sites for turtles: green and hawksbill turtles are regularly seen resting under ledges or feeding on the bommies, and loggerheads turn up occasionally. Photographers will find plenty of structure for wide-angle framing, and the shallow clam garden is ideal for a long safety stop. The maze-like layout means it is best dived with a guide or with a buddy who is confident with a compass, but the maximum depth and mild conditions make it suitable for newly certified divers.

It is also a good second or third dive of the day after a deeper wall. Snorkellers can enjoy the shallow bommie tops and clams when the tide is up.

Boat access only. Cairns day boats leave from the Reef Fleet Terminal (1 Spence Street) and the neighbouring Marlin Marina on the city waterfront, with check-in between about 7:00 and 8:00 am; most operators run transfers from city and northern-beaches accommodation, and there is paid parking near the terminal. The run of about 57 km out through Trinity Inlet and across the lagoon to Flynn Reef takes around 80 minutes on a fast catamaran and noticeably longer on slower dive boats or into a south-easterly chop.

Gordon's Mooring is one of several Flynn moorings used by Silverswift and the Pro Dive Cairns liveaboard; the choice is made on the day. Kit up during the trip out and enter from the stern platform.

The prevailing south-east trade winds (typically 15-25 knots from April to September) are what limit Cairns outer-reef diving: above about 25 knots trips may be cancelled, and exposed eastern moorings are used only in light winds. Summer northerlies are gentler but make north-facing moorings choppy. Box jellyfish and Irukandji are present from about November to May (stinger suits on every dive), and the cyclone season runs November to April, when a system in the Coral Sea can close the reef for days.

Visibility drops after heavy rain and strong winds; spring is usually calmest and clearest. Gordon's is fairly well protected in south-east trades; surge can reach the shallow bommie tops in strong winds, so the deeper swim-throughs are the place to be on rougher days.

Drop down the mooring to around 12 m, then weave a loose circuit between the bommies, using the swim-throughs and overhangs at 10-18 m. Keep the boat's position in mind as the bommies look alike. Finish on the giant clam garden in 5-8 m and do your safety stop there.

Silverswift (Silverseries) – daily day trips, three dives, rotating between Flynn, Milln, Thetford and Pellowe; Passions of Paradise – daily sailing-catamaran day trips to Flynn moorings; Pro Dive Cairns – 3-day/2-night liveaboard, sites on Flynn, Milln, Thetford and Pellowe including night dives