Myrmidon Reef lies on the eastern rim of the Great Barrier Reef off Townsville, where the continental shelf falls away into the Coral Sea. It is the outermost reef in the Townsville sector and an AIMS long-term monitoring site, carrying an automated weather station tower. For divers it offers an experience quite unlike the mid-shelf day-trip reefs: clear oceanic water, big walls and a strong pelagic presence.

The Marine Life Network describes a reef of caves, crevices and canyons, with multiple flanks cut by gullies, overhangs, bommies, walls and swim-throughs, generally dived at 20 m and more. Visibility of 10–30 m is typical, and the water clarity lets divers see well down the walls. Giant clams sit on the shallower terraces, turtles and stingrays are common, sharks patrol the edges, and pelagic fish move along the drop-offs, while the reef fish community – surgeonfish, damselfish, parrotfish, coral trout, fusiliers – is abundant.

The reef took damage in Cyclone Yasi in 2011 and was reported as recovering. Myrmidon's exposure is both its appeal and its problem. It needs calm weather, can have strong currents and is a long way from port, so it is not visited by day boats.

In the heyday of Townsville liveaboards it featured on multi-day circuits; today it is reached mainly on occasional liveaboard or long-range charters, sometimes combined with the Yongala. For experienced divers who get the chance, Myrmidon offers the closest thing to Coral Sea-style wall diving within the Townsville region, with the bonus of clear water and larger animals. Documentation of individual named sites is limited, and current operator coverage should be checked before planning.

Boat only, and beyond normal day-trip range. The outer Townsville reefs lie 90–130 km offshore; they are reached by liveaboard or extended charter from Breakwater Marina, Townsville (typically an overnight steam or 3–4+ hours by fast vessel), sometimes combined with the Yongala on multi-day itineraries. Private skippers need a capable offshore vessel, long-range fuel, EPIRB and a settled forecast, and should launch from the Townsville Breakwater or Ross River ramps.

There is no shelter on the passage and anchoring must be on sand, never coral.

Myrmidon sits on the outer edge of the reef, exposed to Coral Sea swell and the full south-east trade winds. It is only diveable in genuinely calm conditions – winds under about 15 knots and low swell – which occur most often in the October–December build-up and in occasional winter lulls. Currents along the outer walls and around the flanks can be strong, especially on spring tides, so dives are usually drifted with boat cover.

Visibility is typically 20–30 m, the best in the Townsville system, and is little affected by coastal floods. Marine stinger season (box jellyfish and Irukandji) runs roughly November to May – wear a full-length stinger suit or wetsuit with hood and gloves, carry vinegar. Cyclone season November–April; tropical lows and cyclones can close sites and damage coral (TC Yasi 2011, TC Debbie 2017).

Drift the outer wall or a flank with the current at 15–25 m, exploring caves, gullies and overhangs, deploy an SMB and ascend along the wall for a safety stop, with the boat following.

No scheduled day trips. Visited on occasional liveaboard and long-range charters out of Townsville (e.g. Adrenalin Snorkel & Dive liveaboard/charter departures, private and club charters).

Historically on Townsville liveaboard circuits of the 1980s–2000s.