Three important rivers flow through the district. These rivers originate from various mountains of the Western Ghats mountain range. The Pamba (), which is the third longest river in Kerala, has its origin in Pulachimala. The Achankovil river () originates from Pasukida Mettu, and Manimala river () originates from the Thattamalai hills. A small portion of Kallada river also falls in the southern border of the district. Pamba and Achankovil rivers together drain more than 70% of the total area of Pathanamthitta.