Coronation Corner marks the southern end of Agincourt Reef No. 3. The published site notes are brief – located at the southern end of reef three, with sharks, cuttlefish, barracuda, sweetlips and fusiliers – but a corner on an outer ribbon reef is a predictable formula: current wrapping around the point, clean oceanic water, and a steady procession of fish. The reef slopes and steps down from about 5 m to around 25 m on the corner, with hard coral on the upper slope and more sea fans and soft corals where the current is strongest.

Visibility is among the best in the Agincourt group, often around 20 m and sometimes reaching 40 m on neap tides and calm days, and it is this clarity that makes the corner special: you can hang off the edge and watch fish moving along the reef well into the distance. Reef sharks – whitetips and greys – patrol the edge, chevron barracuda hang in a school off the point, and sweetlips cluster under overhangs on the slope. Fusiliers stream past in the current, attracting trevally.

Closer to the reef, cuttlefish are common, often seen hovering near coral heads or displaying to one another. The dive is usually run as an out-and-back from the mooring, heading towards the corner while you are deeper and returning shallower along the slope. If the current is running hard on the point, guides will turn early or keep the group in the lee.

That makes the site better suited to divers with some experience of mild current, although in calm conditions it is accessible to newer open water divers staying shallow. Coronation Corner is a good choice when you want a slightly more exposed, fishier dive than the lagoon sites, without committing to the full depth of the Agincourt walls.

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.

Descend near the corner and work along the reef edge at 15–20 m towards the point, watching the blue for sharks and barracuda. Turn on half your gas or when the current starts to pick up on the point, and return shallower at 8–10 m along the reef slope to the mooring for a safety stop.

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.