Rivers of Kerala are small by all India Standards. There are 44 rivers in Kerala based on a yardstick of 16 KM length to designate a natural channel as rivers. 

Out of these 44 rivers, 41 rivers are follows westward to the Lakshadweep Sea. There are some streams such as the Kumbala, Kalnad, Bekal and Pooramparamba has separate watershed and drains into the Arabain sea directly or through the backwaters. 

Some of the west-flowing rivers join together before they outfall, therefore there are 34 river basins drained by 44 rivers. There are 10 rivers that originated outside Kerala. Periyar is the longest river of Kerala and Bharathapuzha, which originates from Tamilnadu is the longest among rivers that flow through Kerala. Manjeswaram river of 16 Km is the shortest river in Kerala.

There are only 11 rivers having length more than 100 KM length. They are Periyar (244 KM), Bharathapuzha (209 KM), Pamba (176 Km), Chaliyar (169 KM), Chalakudy (130 KM), Kadalundi (130 KM), Achancovil (129 KM), Kallada (121 KM), Muvattupuzha (121 KM), Valapattanam (110 KM) and Chandragiri (105 KM).

Drainage pattern of Kerala is dendritic indicating the dominance of hard crystalline rocks. Radial drainage pattern in Kerala is associated with the granitic bodies. There are evidences of drainage rearrangement and river capture in the foothill region. River capture is evident in case of Ithikara and Kallada rivers. 

While all other rivers are originated from the higher altitude of the Western Ghats, Ithikara is originated from the altitude less than 600m. Ithikara has lost its headwater to Kallada through river piracy

Achenkovil is an Antecedent River. It is draining one of the world’s oldest troughs of Precambrian origin.