A lagoon is a shallow water body separated from a larger water body by Islands or reefs or shallow ridge. Chilika lake is the largest brackish water lagoon in India and is also the estuary of River Daya draining into the Bay of Bengal. A 32 km long channel forms the mouth of the river joining the sea. This estuarine region is a unique combination of freshwater, brackish water and marine ecosystems. The wetland ecosystem of Chilika is the first Indian wetland of international importance under the Ramsar Convention.