Brown reefs edge a turquoise lagoon in this astronaut snapshot of the New Caledonian coastline. Reefs like these form a natural barrier that protects coastlines from storms by breaking up waves (seen here as those white edges) before they reach the shore. The lagoon is streaked with lines of tan where sediment flows from the uplands into the water. Similarly, the color variations from green to blue in water hint at changes in depth, organic content, and more. (Image credit: NASA; via NASA Earth Observatory)