Koshi Tappu Wildlife Reserve lies on the flood plains of 
the  Sapta -Koshi in Saptari and Sunsari Districts of Eastern 
Nepal  . The reserve is  defined  by  the eastern and western 
embankments of the river.

     Rapid  and  complete inundation of the reserve to depths 
ranging  from  10  to  300  cm occurs during the monsoon. The 
Sapta  - Koshi  river also changes its course from one season 
to another

     The  vegetation  is mainly tall kharpater grassland with 
a  few  patches  of  khair -sissoo scrub forest and deciduous 
mixed  riverine  forest. The reserve offers important habitat
for a variety of  wildlife . The  last  surviving  population 
( about 100 )  of wild  buffalo or arna are found here. Other
mammals  are  the  hog  deer ,  wild  boar, spotted deer, and 
the   blue  bull . The   reserve  also   assists   the  local 
economy  by  providing  fishing  permits  and  allowing   the 
collection of edible fruits and ferns in season

     A  total  of  280  different  species of birds have been 
recorded  in  the  reserve. These include 20 species of ducks,
two  species  of  ibises , many storks,egrets, herons and the
endangered  swamp  partridge  and  Bengal florican. The Koshi
Barrage  is   extremely  important   as  a  resting place for 
migratory  birds . Many  species  recorded  here are not seen 
elsewhere   in  Nepal . The endangered  gharial crocodile and 
Gangetic dolphin have been recorded in the Koshi River.