The naturally undulating terrain of Bangalore city, with its hills and valleys, lends itself perfectly to the development of lakes that impound rainwater, store it for future use and ensure ground water recharge. Lakes are thus live ecological systems, and play a crucial role in the supporting life, including human.
Lakes in Bangalore were designed in cascades from higher to lower elevations; as a lake overflowed the excess water would flow into the next lake in the cascade. The flow of water is from North to South-east as well North to South-west along the natural gradient of the land.
Bangalore has three main valley systems: Hebbal, Koramangala - Challaghatta, Vrishabhavati. The lakes thus form a chain of reservoirs in each of the three valley systems. Each valley at the ridge top gives birth to small streams. These cascade down to form major stream systems in three valleys. The valleys are thus the repository of all the lakes in Bangalore and these lakes themselves are interlinked to each other through a series of chains of lakes giving a cascading effect to the whole system.
Lakes are critical to the city of Bangalore, as it does not have any perennial river (Cauvery river is about 140 km away). However, unplanned urban growth, encroachments, pollution and other human interventions have endangered these lakes. Till 1960, there were 262 water bodies in Bangalore, today these have declined to about 81 of which only 34 are recognized as live lakes. The reduction of water bodies is as high as 35%, while in terms of water spread area, it shows a decrease of 8.66 percent.
These maps from the website of the ENVIS Centre - Department of Ecology and Environment (Govt of Karnataka) show the cascade series of lakes. The attached spreadsheet file gives the area in hectares of all the major lakes of Bangalore.