Koonthankulam Bird Sanctuary or Kunthankulam is an important human-made wetland in the state of Tamil Nadu. Spreading over 72.04 ha, the wetland is located near Koonthankulam village in Nanguneri Taluk of Tirunelveli district. The wetland was declared as a bird sanctuary in 1994 and comes under the jurisdiction of Tamil Nadu Water resources department (PWD) and Tamil Nadu Forest Department, Tirunelveli district. This is the largest reserve for breeding resident and migratory water birds in South India. It is an Important Bird and Biodiversity Area forming part of the Central Asian Flyway, code: IN269, criteria: A1, A4i. The inland tank was built few centuries ago, interconnected by canals that bring water from the rivers originating in the Western Ghats. These rivers and tanks support rich social and cultural heritage and economically support agriculture, the major source of people\\\\\\\'s livelihood. There are two outlets on the eastern side for water regulation and irrigation. It irrigates about 190 acres of paddy. While socio-economic and cultural significance exist, very little is known about their ecological importance. The site experiences tropical humid climate, receiving water only through seasonal rainfall ranging from 750-850 mm. The wetland supports a rich diversity of flora-mix of trees, shrubs, herbs, climbers, creepers and pteridophytes. At least 69 floral and 92 faunal species have been recorded from the site. Presence of IUCN classified near threatened migratory birds makes the site important and requires long-term conservation of water birds, besides being part of Central Asian Flyway. The major sources of water for the wetland is rainfall, groundwater, surrounding runoff from catchment and Manimutharu Dam, enhancing groundwater recharge. The wetland acts as a sink for sediments. This wealthy ecosystem has presently come under threat because of encroachments, increasing shrimp farms and other anthropogenic activities.

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.