Photo by @CristinaMittermeier // A coral reef that grows in the rough shape of a ring, often around an inactive volcano, is known as an atoll. The volcano sinks underwater, but the coral grows close to the surface, creating a lagoon inside a chain link of small coral islands. In this photo, a boy swims in the waters of Rangiroa, an atoll in French Polynesia famous for its clear blue water and diverse marine fauna. Rangiroa has 415 islets made out of coral; people live year-round on two of them. Roughly 75% of the world's coral reefs are in distress; threatened by warming water and climate change. The reefs around French Polynesia have not gone unaffected, but there are people working every day to lessen the impact of local and global pressures on these island reefs.