Sonadia is a crescent shaped island off the Cox's Bazar coast. The area of the island is about 9 sq. km. Its western coast is sandy and is rich in different kinds of shells. At the northern part of the island, there are beds of windowpane oysters.

During winter, fishermen set up temporary camps on the island and dry sea fishes, which they catch from the sea. Every winter thousands of fishermen camp there and make large hauls.

The island is also known as a paradise for migratory birds like ducks, sea-gulls, fowls and geese etc. During the winter season migratory birds in swarms are found crowding the beach, marshes and pools of the island.