There are four drainage areas in the park which are vital catchments for four river systems. The Takhong River drains from the central Khao Yai area and runs in a northeasterly direction to the Mekong. The Sai Yai system drains from the eastern basin, turning sharply into the southern floodplains and on to the Gulf of Thailand. The Nakhon Nayok river system drains from the southwest watershed into Nakhon Nayok Province to the south. The Saraburi Province drainage system drains westward from the far west of Khao Yai.