The Kaliveli wetland is unique in many ways: it is a seasonal wetland with a salinity gradient from fresh to brackish water; it is an important stop on the migratory flyway; and it is a breeding ground for many species of water birds. The watershed includes diverse landforms such as the coast, dunes and charnockite hillocks. The plateau supports the last vestiges of the TDEF. The Kaliveli tank and the Yedayanthittu estuary are situated about 20 km north of Pondicherry along the coast towards Marakkanam in the Villipuram district of Tamil Nadu. Broadly speaking, three wetland ecosystems exist in the area: the floodplain, the mangroves and the estuary.