Lakes and tanks in the metropolitan area of Greater Bangalore and the district of Bangalore Urban are reservoirs of varying sizes constructed over a numb er of centuries by various empires and dynasties for rainwater harvesting. Historically, these reservoirs were primarily either irrigation tanks or for the water supply, with secondary uses such as bathing and washing. The need for creating and sustaining these man-made dammed freshwater reservoirs was created by the absence of a major river nearby coupled with a growing settlement. As Bangalore grew from a small settlement into a city, both of the primary historical uses of the tanks changed. Some lakes have been redefined as recreational spaces. Some have been built upon. Other lakes have reduced in size and are in various stages of deterioration. While associated pollution is rampant such as the case of Bellandur Lake which is used as a sewage tank, numerous public and private efforts have been undertaken to address sewage treatment, prevention of dumping and encroachment.

Source: Wikipedia