Nila River is one of the most famous rivers of Kerala. Mamankam is a celebration held every 12 years at Thirunavaya in Malappuram on the banks of this river. Mamankam began during the reign of the Samoothiri Raja . The monuments of the ancient times at Thirunavai are still standing. The monuments are Manikinar, Chenganpilly Kalari, Pazhaka Mandapam and Standing Floor.