Tulsi Lake is a fresh water lake in northern Mumbai. It is stated to be the second largest lake in Mumbai and supplies part of the city’s potable water. This is one of the three lakes located in the Salsette Island; the other two being Powai Lake and Vihar Lake . Both Tulsi lake and Vihar lake are located within the densely forested Sanjay Gandhi National Park or also known popularly as the Borivali National Park (BNP).
Tulsi Lake was built by damming the River Tasso, and redirecting the flow to the nearby Vihar Lake. Rain water from the the catchment area of 676 hectares of Powai-Kanheri hill ranges drains into the lake. During the rainy season the flood flows out flows into the Powai Lake and further down in to the Mithi River. The maximum height of hill in the catchment is about 400 m. The southwest monsoon sets in by mid June and lasts till September. The maximum rainfall is normally recorded in the months of July and August. The mean annual rainfall is reported to be 2500 mm. The plan to create the lake was conceived in 1872 A.D and construction completed 1897 A.D. It was designed as a back up for the Vihar Lake. The lake has surface area of 1.35 sqkm (135 hectares). The average water depth is reported to be 12 m with a gross storage at Full Supply Level (FSL) of 2294 million gallons, out of which 4 million gallons per day are supplied to Greater Mumbai . The highest overflow level, recorded at the dam is 139.17 m (456.6 ft).This fresh water lake primarily fulfills the water requirement of the southern part of Mumbai..
The vegetation on the hill slopes draining into the lake is thick and lush, undisturbed and of mixed moist deciduous type. The lake and its catchment are protected by the Brihadmumbai Municipal Corporation and Sanjay Gandhi National Park Authority. As the lake is situated inside the Sanjay Gandhi National Park, the flora and fauna reported for the park would be relevant to the lake. However, fresh water crocodiles Mugger or Marsh crocodiles (Crocodilus palustris) are known to inhabit the lake in sustainable numbers. As it is difficult to sight them in the lake, the park has set up a Crocodile Park’ to view the reptiles of different sizes