Periyar River which has a length of 244 kms is the longest river in Kerala. It is a perennial river and is used for supplying drinking water. It is popularly called as the Lifeline of Kerala. Periyar River originates from Sivagiri hills of Western Ghats and flows through the Periyar National Park and reaches the Periyar Lake. The water from here then flows into the Vembanad Lake and then finally to the Arabian Sea. A portion of the water from the lake is diverted through a tunnel into the Vaigai River in Tamil Nadu state. This water is used for supplying drinking water in almost 5 drought affected districts in Tamil Nadu. The Periyar Lake dam is maintained by the Tamil Nadu government based on an agreement between the two states.