The Koshi Tappu wildlife reserve is a paradise for bird watchers, with an area of 175 square kilometers. The park is situated on the bank of the Sapta Koshi River.  The vegetation here is mainly of wetland grassland, scrub and deciduous forests. The reserve is unique for its wild buffaloes (Arna). Other mammals visible in the reserve are the hog deer, wild boar, spotted deer and blue bull. The species of birds total 350 here, including 20 of ducks, many storks, egrets, herons, and the endangered swamp partridges and Bengal floricans. The reserve is resting place for migrating birds not seen anywhere in Nepal. The endangered gharial, marsh crocodile and Gangetic dolphin are also recorded in the Koshi River.