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Bharatapuzha(River Nila) is the longest river in Kerala, 209 of its 250 km course flowing through the state. The river originates from the Thirumurthy Hills of Anamalais in Tamil Nadu state at an elevation of 1964 m above mean sea level. It flows through Coimbatore district in Tamil Nadu and Palakkad,Thrissur and Malappuram districts in Kerala. The river drains into the Arabian Sea at Ponnani in Malappuram.
It has an extensive catchment area of 6186 Sq. Km. River Bharathapuzha is bestowed with a rich web of tributaries and sub-tributaries. The river basin receives an average annual rainfall of 2,300 mm and the annual average stream flow is estimated to be 5,082.9 million cubic metres. About 40 Km of the main stream is navigable.