The lake in Tamil Nadu's Tiruvallur district is home to 160 different fish species and more than 110 varieties of terrestrial and aquatic birds and small mammals and reptiles.
About 15,000 flamingos visit the lake on their annual migration route.
More than 60,000 migrant water birds feed and breed in the northern part of lake during winter. About 40,000 people living in 34 villages on the banks of the lake on the Tamil Nadu side, depend directly or indirectly on the lake.
The survey, 'Pulicat Community Based Disaster Preparedness conducted recently by an expert team of the Loyola Institute of Frontier Energy revealed that the lake area, which once extended to 460 square km, has reduced to 350 square km in a few decades, leading to a huge reduction in aquatic population.
This was due to rapid shrinking of the water spread area mainly due to silting in the lake's northern part.Earlier the lake's depth used to be four metres, but now it is 1.5 metres. This has led to "lower aquatic life", Project Chief Co-ordinator Dr Selvanayagam told PTI.
He said during summer, sea water inflow decreases and evaporation due to summer heat saturates the salinity of the lake water.
Pulicat Fishermen association member Kandasamy said extensive use of nets with small mesh also takes away sea plants while fishing. "Earlier, there were some restrictions on night fishing. But today no one is following the rules and regulations", he said.The study said motor boats are used indiscriminately in the lake where only paddle and row boats were used earlier.
The lake traffic continues throughout the day and night and this unsettles both aquatic and bird life thereby affecting the ecology, it said.
The study has demanded setting up of an independent organisation on the lines of the Chilka Lake Development Authority in Orissa for managing Pulicat.Global Nature, a German-based NGO, which deals with protection of environment and nature, has described Pulicat Lake as "Threatened Lake of the Year 2010".
"The once species-rich fishing grounds and the ecologically important mangrove forests in the lagoon north of the city of Chennai have reached an alarming dimension," it said in a recent communique.
The organisation also claimed that over-exploitation, mismanagement as well as improperly treated industrial effluents (containing heavy metals) from more than 25 industries from neighbouring Chennai deteriorate the water quality.
The organisation said that in Andhra Pradesh around 4700 hectares have been allotted for a marine chemicals and salt manufacturing industry while on the Tamil Nadu side, a petrochemical complex, power plant and the satellite port on Ennore Creek were major ecological threats.
Earlier there were around 30,000 fishermen in the area but due to lack of jobs, thousands of farmers and labourers living in the lake region started fishing in the lake, particularly after the Tsunami in 2004.
Prawn farms and an increasing population put additional pressure on the lake’s ecosystem. Overuse of the natural resources and shortage of clean drinking water are inevitable consequences, the organisation said.