Periyar is the longest river in the state of Kerala

Kerala

or Keralam is an Indian state located on the Malabar coast of south-west India. It was created on 1 November 1956 by the States Reorganisation Act by combining various Malayalam speaking regions....

, India

India

India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

, with a length of 244 km. The Periyar is known as the lifeline of Kerala; it is one of the few perennial

Perennial stream

A perennial stream or perennial river is a stream or river that has continuous flow in parts of its bed all year round during years of normal rainfall. "Perennial" streams are contrasted with "intermittent" streams which normally cease flowing for weeks or months each year, and with "ephemeral"...

 rivers in the region and provides drinking water for several major towns. The Idukki Dam

Idukki Dam

The Idukki Dam, located in Kerala, India, is a 555 foot tall arch dam. The dam stands between the two mountains - Kuravanmala m and Kurathimala m. It was constructed and is owned by the Kerala State Electricity Board....

 on the Periyar generates a significant proportion of Kerala's electrical power.
Periyar originates in the Sivagiri hills of the Western Ghats

Western Ghats

The Western Ghats, Western Ghauts or the Sahyādri is a mountain range along the western side of India. It runs north to south along the western edge of the Deccan Plateau, and separates the plateau from a narrow coastal plain along the Arabian Sea. The Western Ghats block rainfall to the Deccan...

 range of Tamilnadu.