Pulicat Lake

Pulicat Lake is the second-largest brackish-water lagoon in India (after Chilika Lake), measuring 759 square kilometres (293 sq mi). A major part of the lagoon lies in the Tirupati district of Andhra Pradesh. The lagoon is one of three important wetlands that attracts northeast monsoon rainclouds during the October-to-December season. The lagoon comprises the following regions: Pulicat Lake (Andhra Pradesh and Tamil Nadu), Marshy/Wetland Land Region (AP), Venadu Reserve Forest (AP), and Pernadu Reserve Forest (AP). The lagoon was cut across in the middle by the Sriharikota Link Road, which divided the water body into lagoon and marshy land. The lagoon encompasses the Pulicat Lake Bird Sanctuary. The barrier island of Sriharikota separates the lagoon from the Bay of Bengal and is home to the Indian Space Research Organisation's Satish Dhawan Space Centre.

In the 1st century, the anonymous mariner who wrote Periplus of the Erythraean Sea listed Podouke (Pulicat) as one of the three ports on the east coast of India. In the 2nd century, Ptolemy's list of ports on this coast included Podouke Emporion.

In the 13th century, Arabs migrated to the shores of the lagoon after they were banished from Mecca for refusing to pay tributes to a new caliph. Streets with dilapidated masonry houses once occupied by these Arab Muslims are still found in the area and resident families claim records in Arabic testifying the migration.

The Portuguese colonized the lagoon in 16th century, followed by the Dutch. The Dutch drifted to the lagoon as their ships got stuck on the shores of Karimanal village on the opposite side of the mouth of the lagoon. During the Dutch occupation, Pulicat was known by the name Pallaicatta. Fort Geldria dating to 1609, a church, a cemetery with tombs, and mausoleums constructed by the Dutch are protected by the Archaeological Survey of India (ASI). The Dutch transacted business with the British East India Company and other countries in the region.

A scientific study of the palynological characteristics of the lagoon was conducted by taking sedimentary soil samples from four test pits. It shows that the vegetational reconstruction from peat beds at 4.98 metres (16.3 ft) a.m.s.l. and 1 metre (3.3 ft) (a.m.s.l.) in the west at Sullurpeta and Kasdredinilem, respectively, is indicative of a palaeoshoreline. The sea level reached its maximum around 6650 ± 110 years BP in Sullurpeta, 18 kilometres (11 mi) west from the present shoreline. The radiocarbon dates of peat bed at Kasdreddinilem reveal an age of 4608 ± 122 years BP, indicating the shift in mangrove line eastwards during the regressive phase.

The lagoon's boundary limits range from 13.33° to 13.66° N and 80.23° to 80.25°E, with a dried part of the lagoon extending up to 14.0°N, with about 96% of the lagoon in Andhra Pradesh and 3% in Tamil Nadu. The lagoon is aligned parallel to the coast line with its western and eastern parts covered with sand ridges. The area of the lagoon varies with the tide, from 450 square kilometres (170 mi²) at high tide to 250 square kilometres (97 mi²) at low tide. Its length is about 60 kilometres (37 mi), and its width varies from 0.2 kilometres (0.12 mi) to 17.5 kilometres (10.9 mi). The climate of the lagoon's coastline is dominated by tropical monsoons. Its air temperature varies from 15 °C (59 °F) to 45 °C (113 °F). The large spindle-shaped barrier island named Sriharikota separates the lagoon from the Bay of Bengal. The sandy barrier islands of Irkam and Venad and smaller islands in the north are aligned north-south and divide the lagoon into eastern and western sectors. The morphology of the lagoons is categorized under four types, with large areas under mudflats and sandflats. The fishing village of Pulicat is at the south end of the lake. The Satish Dhawan Space Center is located on the north end of the island. Pulicat, Dugarājupatnam, and Sullurpeta are villages located on the periphery of the lagoon.

Two rivers which feed the lagoon are the Arani River at the southern tip and the Kalangi River from the northwest, in addition to some smaller streams. The Buckingham Canal, a navigation channel, is part of the lagoon on its western side. The lagoon's water exchange with the Bay of Bengal is through an inlet channel at the north end of Sriharikota and an outflow channel of about 200 metres (660 ft) width at its southern end, both of which carry flows only during the rainy season. The lagoon acts as a buffer to retain the accumulated floodwater until the floodwater is discharged gradually to the sea during the monsoon period and cyclones. The lagoon and its river basins are located both in Andhra Pradesh and Tamil Nadu. The lagoon and its drainage river basins are interstate river basins as per the Interstate River Water Disputes Act of 1956. Most of the lagoon area, including its water outlet to the sea, is located in Andhra Pradesh.

The water quality of the lagoon varies widely during various seasons – summer, pre-monsoon, monsoon and post-monsoon – as the depth and width of the lagoon mouth varies, causing a dynamic situation of mixing and circulation of waters. The resultant salinity variation and dissolved oxygen affects the primary production, plankton, biodiversity, and fisheries in this lagoon. Salinity values vary from zero during the monsoon to about 52,000 ppm (hypersaline) during the post- and pre-monsoon seasons. Adjustment to this wide variation is difficult for sessile and sedentary species in the lagoon. However, euryhaline species still dwell in the lagoon. The benthic or bottom habitat of this lagoon is classified into three zones: the southern zone is dominated by sand with some admixture of mud, the northern zone is wholly muddy, and the third zone with sand and mud in equal parts is overgrown with patches of weeds and is reported to be rich in benthic biodiversity. Toxicity levels of heavy metals such as magnesium, lead, zinc, nickel, cadmium, aluminum, and copper and chemicals such as ammonia, sulphate, and fluoride in the lagoon are well within permissible limits. Recently, the lagoon likely experienced up to 40% desalination due to the impact of freshwater floods from the 2015 South India floods.