Estuary is a place where freshwater from a river meets and mixes with saltwater from the sea. This creates water that is partly salty and partly fresh. Estuaries often have changing water levels due to tides. They can include mudflats, marshes, and channels.

Estuaries are found along coastlines around the world. They are part of coastal water systems and exist over long periods. Estuaries support many plants and animals, including fish and birds. They are important environments for many living things.