Coral might look like a colourful rock or plant, but it is actually made of tiny animals called polyps. Each polyp is no bigger than a grain of rice. Over thousands of years, millions of them build hard skeletons that join together into reefs. The whole Great Barrier Reef has been built by these tiny creatures.
The reef is home to about 1,500 different kinds of fish, six kinds of sea turtle, dolphins, manta rays, and even small reef sharks that mostly mind their own business. There are clownfish like Nemo from the film, and giant clams as big as a bath.
Coral needs warm, clean, sunny water to grow. The reef has dozens of bright colours: yellow staghorns, purple brains, soft pinks and bright oranges. Scientists who study the reef say swimming through it is a bit like flying through a giant underwater garden.
The Great Barrier Reef is so important that the whole world helps look after it. Reef rangers, scientists and local communities work together to keep the water clean and to plant new coral where some has been damaged. Many Australian schools 'adopt' a piece of reef to look after.