Neyyar River flows through Thiruvananthapuram district. It originates from Agastyarkoodam hills and then passes through Neyyattinkkara. It then finally empties into the Arabian Sea. The river has a length of 56 kms. Some of the main tributaries of this river are Kallar, Mullayar, Karavaliyar River etc. There are many canals in this river some of which are Kulathoorvaliathode, Athiyanurthode, Thalayilthode, Venganurthode etc. It is on this river that the Neyyar Irrigation Project is commissioned at Kallikkadu.

The Neyyar wildlife sanctuary and the Safari park lie near this river. It is a famous tourist destination. Tourists can go for boating in this river. Neyyar dam is located in the Neyyar River. The construction of a dam leads to the formation of a lake which has very clear blue waters. Neyyar wildlife sanctuary forms the drainage basin of the river.