A Coastal wetland of Natural origin located in the Dry Zone of the Northern province.The Jaffna lagoon is a semi-enclosed water body connected to the Palk Bay . It is surrounded by a dry zone land mass and due to being more greatly influenced by freshwater input, has different physical conditions to that of the larger Palk Bay . The lagoon contains a number of coastal wetland habitats and is an important breeding area for numerous marine species. Jaffna lagoon has been identified as an IBA by BirdLife International. The lagoon opens into the north eastern part of Palk Bay by way of three narrow openings and one wide opening, and is also influenced by tides in the Bay. The lagoon is long and narrow, extending from Elephant Pass in the southeast to Kayts in the northwest. The lagoon is relatively shallow with the maximum depth being less than 3 m. The shoreline is composed mostly of sandy soil while the bottom is mostly mud. The salinity in the lagoon is greatly influenced by rainfall and freshwater run-off from surrounding areas, and varies from a low of around 10.3 ppt during the rainy season to a high of around 45.49 ppt during the dry season. The lagoon is located in the dry semi-arid zone with an average temperature of around 270 C and an annual rainfall between 500-700 mm. Most rain is received during the northeast monsoon from October to February. The lagoon and adjoining areas are important for numerous waterbirds. Fisheries are currently restricted due to the security situation and would increase if the security improves in the area. Vegetation such as mangroves is liable to be cleared for security reasons. The lagoon plays a role in flood control during times of heavy rainfall. Being part of the larger Palk Bay area it plays an important role in regimenting tidal movements, currents and salinity in surrounding water bodies. Fisheries have been important economic activities of coastal communities, and many are engaged in small scale fisheries using traditional methods such as cages, traps and cast nets. Clearing of shoreline vegetation for security reasons has degraded much of the mangroves in the area. The development of the Sethusamudram Ship Canal is also likely to impact upon the ocean circulation, physical conditions and biological cycles within the Palk Bay area, and could affect the biodiversity and biological cycles within the lagoon.

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