The Great Barrier Reef runs for more than 2,300 kilometres down the Queensland coast — the largest structure on Earth built entirely by living creatures, raised not over millions of years but over the last six to eight thousand, by billions of coral polyps each no bigger than a fingernail. It is not one organism but a vast mosaic: around 2,900 separate reefs and 900 islands, sprawling across an area larger than Italy and visible from space. UNESCO inscribed it as a World Heritage Site in 1981 under all four natural criteria, and it is easy to see why — more than 1,500 species of fish, six of the world's seven marine turtle species, giant manta rays, reef sharks and dugongs all share this single shallow sea.
Slip beneath the surface and the scale you could never sense from a boat comes into focus. Turquoise shallows drop away as if drawn with a ruler; coral gardens spread in mustard yellow, lilac and rust, and clouds of fish drift between them. Snorkellers hang above whole terraces of coral while divers follow the reef walls out to the drop-off, where the water darkens to deep blue. Off the Whitsunday Islands, a small heart-shaped tangle of coral barely seventeen metres across — Heart Reef — has become the reef's signature image. But this is a living thing changing in front of us: warmer seas have brought repeated mass bleaching in recent years, and stretches once brilliant have paled. Much of the coral still teems with life and recovers, yet a visit today means seeing a wonder that is neither eternal nor guaranteed.