The Koyna River is a tributary of the Krishna River which originates in Mahableshwar, Satara district, western Maharashtra, India. It rises near Mahabaleshwar, a famous hill station in the Western Ghats. Unlike most of the other rivers in Maharashtra which flow East-West direction, the Koyna river flows in North-South direction. The Koyna River is famous for the Koyna Dam and the Koyna Hydroelectric Project. Today the Koyna Hydroelectric Project is the largest completed hydroelectric project in India. The reservoir - Shivasagar Lake, is a huge lake of 50 km in length.