Agincourt Reef

Agincourt Reef sits out past Port Douglas, right where the continental shelf runs out and the seabed simply falls away into deep blue. It is one of the outer ribbon reefs, and unlike most of the reef system, which slopes gradually, here the transition from shallow coral garden to open ocean drop-off happens abruptly enough that you can hover at the boundary and look down into water with no visible bottom. I have snorkelled a lot of reef edges since moving to this side of the world, and this was the first time the depth genuinely made my stomach drop, not from danger but from scale.

Access is by a permanently moored pontoon that day-boats from Port Douglas motor out to, about ninety minutes each way, and the operation is slicker than I expected — marine biologists giving briefings, a semi-submersible for anyone who doesn’t want to get in the water, and a genuinely well-managed crowd given how many people the platform can handle at once. I went with a smaller operator that limits numbers, worth the extra cost, and had a guided snorkel where the biologist pointed out a hawksbill turtle grazing on sponge that I would have swum straight past otherwise.

The coral diversity here is remarkable even by reef standards — plate coral the size of dinner tables, fields of staghorn in improbable pale blues and pinks, clouds of blue-green chromis moving as one nervous unit whenever a bigger fish passed through. Because Agincourt sits so far from shore, the water clarity on a good day is some of the best I have experienced on the whole reef system, closer to aquarium glass than ocean.

When to go: June to November brings the calmest crossing and clearest water. The boat ride out can be rough in windier months, so if you are prone to seasickness, take medication in advance and aim for the earlier, calmer part of the year.