was considerably improved and maintained through the mandatory rain water harvesting system. Of the 24.87 km coastline of the city, 3.08 km experiences erosion, with sand accretion along the shoreline can be noticed at the Marina beach and the area between the Ennore Port and Kosasthalaiyar river. Geology Chennai is classified as being in Seismic Zone III, indicating a moderate risk of damage from earthquakes. Owing to the geotectonic zone the city falls in, the city is considered a potential geothermal energy site. The crust has granite rocks indicating volcanic activities in the past. It is expected that temperatures of around 200 to 300 C° will be available if the ground were drilled 4 to 5 km deep. The region has the oldest rocks in the country dating back to nearly a billion years. Flora and fauna The southern stretch of Chennai's coast from Tiruvanmiyur to Neelangarai are favoured by the endangered olive ridley sea turtles to lay eggs every winter. A large number of cattle egrets, pond herons and other waterbirds can be seen in the rivers of Cooum and Adyar. About 75,000 birds migrate to Chennai every year. Marshy wetlands such as Pallikaranai also play host to a number of migratory birds during the monsoon and winter. Over 300 species of birds have been recorded in the city and its neighbourhood by members of Madras Naturalists' Society since its inception in 1978. Guindy National Park is a protected area within the city limits. Wildlife conservation and research activities take place at Arignar Anna Zoological Park including olive ridley sea turtle conservation. Madras Crocodile Bank Trust is a herpetology research station, located south of Chennai. The city's tree cover is estimated to be around 64.06 sq km. The most dominant tree species is the copper pod, followed by Indian beech and Neem. A total of 121 species of trees belonging to 94 genera and 42 families are found in the city. Nearly half of the native plant species in the city's wetlands have disappeared in recent years. The city, which had 85 percent of its area covered with aquatic plants until the 1970s, now has only 25 percent of its area covered with such plants. Environment conservation Chennai has three rivers and many lakes spread across the city. Urbanization has led to the shrinkage of water bodies and wetlands. The quantity of wetlands in the city has decreased from