The Great Astrolabe Reef, near the island of Kadavu, is one of the largest barrier reefs in the world. It stretches for about 100 kilometres around the island, like a long underwater wall. Inside the wall, the water is calmer and full of sea life. Outside, the ocean drops away into very deep, dark blue.
Coral is not a plant - it is an animal. Millions of tiny creatures called polyps build hard shells around themselves. Over hundreds of years, as one generation of polyps builds on top of another, those shells become a reef. The whole structure is built grain by grain, creature by creature.
The reef's bright colours come mostly from tiny plants called algae that live inside the coral. The algae make food from sunlight and share it with the coral. Together they keep each other alive. When the sea gets too warm, the algae leave, and the coral turns white - this is called bleaching. Scientists around the world work to keep reefs healthy.
Around 1,500 species of fish live in Fiji's reefs, along with sea turtles, sharks, clownfish, giant clams and octopuses. Fijian families have fished these reefs for thousands of years and many communities have their own traditional rules about which areas to rest and let the fish come back.