The Pahang River system is the largest in Peninsular Malaysia. The principal tributaries are Sungai Tembeling, which forms part of the southern boundary of Taman Negara, and Sungai Jelai, on which the jetty for National Park boats is situated. Four hundred metres downstream from the jetty the two rivers join, at Kuala Tembeling, to become Sungai Pahang. From here it is 300 kilometres downstream to the sea, and 60 kilometres upstream, on Sungai Tembeling, to Kuala Tahan.

Along your journey, especially for the first 35 kilometres, you can see Malay villages (kampung) located along both banks, village trees - tall slender betel-nuts palms, coconuts, kapok trees (with short fat pods) and bonglai trees (with extremely long pods), local fishing people, as well as the village buffaloes along the water's edge.

After the Taman Negara boundary is reached, at Kuala Atok, it is National Park on the left, and on your right is the secondary growth and cultivation.

Along the river edge, the most common trees you can see are the red river fig (Ficus racemosa, ara masi) with clusters of fruits, ripening red, along the lower branches;the river jambu (Eugenia densiflora var. agustifolia, jambu air) with creamy-white "asterisk" flowers and round white fruits; the bungur trees (Lagerstroemia speciosa) producing dense upright clusters of bright mauve flowers during the first half of the year.

Though wildlife is not abundant along the river, you will not go unrewarded if you stay alert. Movement of leafy branches often indicates the presence of monkeys; Sometimes, otters are sighted, too Don't be shocked if you see "crocodiles" in the river. They are in fact water monitors-lizards (Varanus salvator) which fully when grown may be two metres long!

Bird-watchers get your binoculars ready! Three kinds of kingfishers with beautiful blue wings are commonly seen. They are the white-throated kingfisher (Halcyon smyrnensis) with a dark brown head and abdomen; the stork-billed kingfisher (Pelargopsis capensis) is larger, with a bright red beak and a very pale brown head; and the black-capped kingfisher (Halcyon pileata) with a red beak and white collar.

During the monsoon season (when Taman Negara is closed to visitors, from mid-November to mid-January) the river level can rise dramatically. When you disembark at Kuala Tahan and climb the concrete steps up the river bank, at the top, please note the marker indicating the flood level on 4th January 1971.