Koshi Tappu Wildlife Reserve lies on the alluvial flood plain of Sapta Koshi River. This, the largest river in Nepal, flows through the reserve. The Sapta Koshi is one of the three main tributaries of the Ganga.
Reverie and Sal forests and grasslands dominate the vegetation of the reserve. This combination of vegetation and wetland proves a special site for birds and animals.
The main mammals here are the Wild Buffalo, Blue Bull and Gangetic Dolphin.
Around 300 species of birds have been recorded in this reserve. These include waterfowl, birds of prey, waders, and other water birds. The globally threatened Swamp Partridge (Francolinus Gularis) is also a familiar sight.
The nearby Koshi Barrage has created a vast expanse of water. This makes it the most important staging point for migrating birds. At the same time it is an all year playground for resident ones.
Makalu, the world's fifth highest mountain (8,463m), can be glimpsed on a clear day. This enhances the beauty of the scenery dramatically.