Turtle Bay is a sheltered bay on the northern end of Agincourt Reef No. 2, and it earns its name: a large loggerhead turtle is regularly seen here in the summer months, according to both Silverseries and Poseidon, alongside green and hawksbill turtles that feed on the reef. The bay is backed by a reef wall decorated with hard and soft corals that drops from about 5 m to sand at around 22 m. The sheltered aspect means calm water inside the bay, while pelagic fish are often seen out towards the reef front where the bay opens to the current.

Along the wall look for sea cucumbers on the sand, giant clams wedged into the coral, whitetip reef sharks resting on the bottom, and sweetlips sheltering under overhangs. Goatfish, chromis and fusiliers fill the water column and parrotfish graze along the reef top. Turtles are the main attraction.

They rest under ledges, graze on sponges and algae along the wall, or surface to breathe beside the boat. Approach slowly from the side, never from above, and keep your distance – they are far more relaxed if you let them come to you. The layout is straightforward: an out-and-back along the wall from the mooring, with the deeper section on the way out and the shallower wall and reef top on the return.

That makes it suitable for new open water divers, and the shallow reef edge gives snorkellers a good chance of seeing turtles too. Visibility is generally around 20 m and occasionally 30 m. Because it is protected from the prevailing south-easterly, Turtle Bay is one of the moorings skippers turn to when the trade winds are blowing.

Divers after a calm, relaxed dive with a high chance of turtles and a nicely decorated wall will enjoy it. Note that there is also a separate site called Turtle Bay on the Sister reefs near Tongue Reef, visited by Wavelength.

Agincourt day boats leave Crystalbrook Superyacht Marina (formerly the Reef Marina) on Wharf Street, Port Douglas, between about 8:00 and 8:30 am. Park in the marina car park or the free all-day street parking around Wharf and Dixie streets; Quicksilver, Poseidon and Calypso also run coach pick-ups from Port Douglas, Palm Cove and northern Cairns beaches. The run to the Agincourt ribbon reefs on the edge of the continental shelf is about 65–70 km north-east and takes roughly 75–90 minutes on the large catamarans (Silversonic is the fastest), longer on small-group boats such as Scuba IQ/Blue Dive.

You gear up on board and giant-stride from the dive deck at a permanent mooring; the skipper picks the sites on the day to suit wind and tide, so a named site is never guaranteed. Boats are back at the marina around 4:30 pm.

Agincourt is an outer ribbon reef on the shelf edge, so it is fully exposed to the south-east trade winds that blow from about April to September. Moorings on the protected western (back-reef) side remain diveable in 15–20 knots, but anything over 25 knots or a 2.5 m+ sea makes the crossing rough and operators may cancel or switch to more sheltered moorings. Calm spells in October–December give the glassiest days and 30 m+ visibility.

The wet season (December–April) brings northerlies, afternoon storms, cyclone risk and occasional reduced visibility after big rain events, although the outer reef is far less affected by run-off than inshore reefs. Marine stingers are present November–May. Tidal currents run along the reef edges and through the gaps between the Agincourt reefs; spring tides strengthen them, so exposed corners are usually dived on the neaps or near slack water.

From the mooring, follow the reef wall at 12–18 m with the wall on one side, checking under ledges for resting turtles and whitetips. Turn on half your gas, return a few metres shallower along the upper wall and reef top, and do your safety stop over the shallow coral near the boat.

Quicksilver Silversonic – daily, 3 dives across Agincourt 1–4; Poseidon (Quicksilver Group) – daily, 3 sites at Agincourt; Calypso Reef Cruises – regular Agincourt days; Scuba IQ / Blue Dive and Tech Dive Academy – small-group day trips several days a week.