Sattal or Sat Tal (Hindi for "seven lakes") is an interconnected group of seven freshwater lakes situated in the Lower Himalayan Range near Bhimtal, a town of the Nainital district in Uttarakhand, India. During the British Raj, the area had a tea plantation, one of four in the Kumaon area at that time. The lakes sit at an altitude of 1370 metres below lush orchards in the Mehragaon valley. Set amongst dense forests of oak and pine trees, Sattal is one of the few unspoiled and unpolluted freshwater biomes in India. These lakes are a paradise for migratory birds. It is home to a few camps being operated mostly by local people catering to tourists looking for outdoor vacations. Geology and physiography Sattal is situated in the Lower Himalayan Range and is the result of tectonic activities and the uplifting of sediments between the Tibetan plain and the Indo-Gangetic plains. The rocks are mainly sedimentary rocks and quartzite. Physiographically the area can be divided into lower Himalayas and terraces. Ecology Sattal is an ecologically fragile mesotrophic group of lakes and under the impact of heavy environmental degradation. Extensive deforestation, dumping of non-biodegradable waste, uncontrolled urbanization of the catchments and nearby forest is harming the ecology of the area. This results in scanty rainfall, a decrease in the number of plant and animal species and rapid drying up of perennial springs. The lakes also suffer from a reduced oxygen content and high levels of nitrogen and phosphorus. Poaching has eliminated many wild animals. Khudariya Tal became Sukha Tal (Dry Lake) due to the leakage of water from its western extremity. An extensive growth of invasive plants such as Lantana, Parthenium and Eichhornia is also endangering the ecological survival of the lakes. Flora and fauna Biological diversity Sattal is unique for its biodiversity and ecological amplitude. It is known to be a birding paradise and supports a number of local and migratory birdlife. It has 500 species of resident and migratory birds, 20 species of mammals, over 525 species of butterflies and over 11,000 species of moths, beetles, bugs and other insects. The flora covers a wide and diverse range of plants ranging from Bryophytes, orchids, rare climbing plants, ferns, lichens, fungi, medicinal herbs and shrubs. Each individual lake has its own unique Diatom index. The Trophic Diatom Index uses the composition of freshwater diatom assemblages to assess water quality and ecological