Lagoon/ləˈɡuːn/ Definition 1 of 2Pro Tip 1/3Natural Formation A lagoon often forms naturally near coastal areas. They went kayaking in the lagoon, enjoying the calm waters. Pro Tip 2/3Protected Waters Lagoons are usually shallow and have calmer water than the open sea. The lagoon was perfect for beginners to practice snorkeling. Pro Tip 3/3Ecological Importance Lagoons can support diverse ecosystems and wildlife. They observed rare birds nesting around the lagoon's edge.