A lagoon is a shallow body of water separated from a larger body of water, such as an ocean or sea, by a barrier like a sandbar, coral reef, or barrier island. These calm waters are often rich in biodiversity and provide a habitat for various species of fish, birds, and plants. Lagoon ecosystems can be found in coastal areas around the world, including famous locations like the Great Barrier Reef in Australia and the Venetian Lagoon in Italy. They play a crucial role in protecting coastlines from erosion and serve as nurseries for marine life.