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.
Due to its electricity generating potential through Koyna Hydroelectric Project, Koyna river is known as the Life Line of Maharashtra
The river meets the Krishna River, which is one of the three largest rivers in southern India by Karad at Pritisangam
The river is just about 100 meters in width and is slow-flowing. It is an olive shade of green during the dry months and a bluish-brown in the monsoon months attributed to much algae and aquatic plant life. The impounded water of the Koyna Dam though has submerged a significant amount of Rain forest of the Western Ghats, it has helped a lot to the surrounding forest by supplying water all round the year. Hence a wide biodiversity of plants and animals is observed in the evergreen forest surrounding the river.