Bhimtal, is the largest of all the lakes covering 72 ha. Lake Naukuchia tal is the deepest of all, with a maximum of 40.8 m. The lake region of Bhimtal, Naukuchiatal and Sattal is unique for its biodiversity since it falls in the blend zone of Paleastic and Indo-Malayan zoo-geography. It boasts 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.  Over the last couple of decades, alarmingly adverse developments had occurred around these lakes which threatened the existence of this ecologically fragile region and the health and economic security of the human population that depend on it. Bhimtal and Naukuchia tal have moderate levels of nutrients. Lake Sattal is poor in nutrients. The lakes have high rates of sedimentation, Bhimtal with 4.70 mm/yr, Naukuchiat al with 3.72 mm/yr, and Sattal with 2.99 mm/yr resulted in less adsorption of heavy metals, leading to their depletion in the bed sediments of the lake.