The lagoon is about 80 kilometres across - big enough to have its own weather inside it. The outer ring of coral keeps the waves gentle inside, so the water is much calmer than the open ocean. This makes it the perfect home for animals that need sheltered water to grow.
Coral reefs are sometimes called the rainforests of the sea, because so many different species live there. On a single coral reef you might spot parrotfish (which actually eat coral rock and poo out white sand), clownfish hiding in sea anemones, moray eels peering out from crevices and hawksbill turtles gliding past.
Coral is not a plant or a rock, even though it can look like both. It is actually made of millions of tiny animals called polyps, each one the size of a grain of rice. The polyps build stone cups around themselves to live in, and over hundreds of years those cups pile up into a whole reef.
The people of Chuuk have fished and sailed these waters for thousands of years. Traditional fishing in Chuuk uses handmade nets and knowledge passed down through families - knowledge about which currents bring which fish, and which times of year the water is best.