Pichavaram mangrove, spanning 1478 Ha, is located between two prominent estuaries, the Vellar estuary in the north and Coleroon estuary in the south. The Vellar-Coleroon estuarine complex forms the Killai backwater and Pichavaram mangroves. The backwaters are interconnected by the Vellar and Coleroon river systems and offer abundant scope for water sports such as rowing, kayaking, and canoeing. The Pichavaram forest not only offers waterscape and backwater cruises but also another very rare sight – the mangrove forest trees are permanently rooted in a few feet of water. Like other mangrove wetlands in India, Pichavaram mangroves support unique diversity of flora and fauna. Two major rivers viz. Vellar and Coleroon drain into the Bay of Bengal in this area. The area between the two rivers is estuarine having brackish water with mangrove vegetation. The mangrove ecosystem acts as a bio-shield during natural disasters, holds and stabilizes shorelines, retards erosion and acts as a buffer zone between land and sea, and helps in adaptation to climate change. The forest habitat is classified as littoral and swamp forest, habitat. It has a natural hybrid species namely Rhizophora annamalayana. It is derived from two species of Rhizophora: R.apiculata and another natural hybrid R.mucronata. This mangrove ecosystem harbors diverse floral and faunal, especially aquatic fauna and wetland birds. The mangroves support several threatened species like Critically Endangered birds like the great white-bellied heron (Ardea insignis), spoon billed sandpiper (Eurynorhynchus pygmeus), Endangered spotted greenshank (Tringa guttifer). The vulnerable Olive ridley turtle lays its eggs every year on the beaches of the Pichavaram coastline. In addition to these 22 species, prawns like Metapeneausaffinis, Metapeneaus brevicornis are also found in the Pichavaram water. This area supports the livelihoods of 1000 families for fishing around this habitat. The mangroves have a significant degree of spiritual value. According to the Sthala Purana, the Sthala Vriksham in Chidambaram Lord Nataraja Temple was the mangrove species Excoecaria agallocha commonly known as Tillai, has been worshipped since the 18th Century. The region used to be called “Tillai Vanam”. Therefore these mangroves are also revered by the local communities.

A wetland should be considered internationally important if it contains a representative, rare, or unique example of a natural or near-natural wetland type found within the appropriate biogeographic region.

A wetland should be considered internationally important if it supports vulnerable, endangered, or critically endangered species or threatened ecological communities.

A wetland should be considered internationally important if it supports populations of plant and/or animal species important for maintaining the biological diversity of a particular biogeographic region.

A wetland should be considered internationally important if it supports plant and/or animal species at a critical stage in their life cycles, or provides refuge during adverse conditions.

A wetland should be considered internationally important if it regularly supports 20,000 or more waterbirds.

A wetland should be considered internationally important if it regularly supports 1% of the individuals in a population of one species or subspecies of waterbird.

A wetland should be considered internationally important if it supports a significant proportion of indigenous fish subspecies, species or families, life-history stages, species interactions and/or populations that are representative of wetland benefits and/or values and thereby contributes to global biological diversity.

A wetland should be considered internationally important if it is an important source of food for fishes, spawning ground, nursery and/or migration path on which fish stocks, either within the wetland or elsewhere, depend.

A wetland should be considered internationally important if it regularly supports 1% of the individuals in a population of one species or subspecies of wetland-dependent nonavian animal species.