The Koshi Tappu (176 sq. km) was established in 1976 to protect the rare wild water buffaloes, Arna (Bubalus arnee). It is a protected area in the Terai of eastern Nepal. This very famous reserve for bird watching is the smallest wildlife reserve in Nepal. In 1987, the Koshi Tappu was declared a Ramsar site, a wetland of international importance.A wide range of faunal species inhabit in the reserve which has important habitat for a variety of wildlife. The government’s last survey has estimated the population of wild buffalos is around 159.

Around 441 species of birds, most of them domestic, have been recorded in this reserve. Other birds found in here includes 20 duck species, 2 ibis species, white tailed stonechat, striated marsh warbler, shore birds, water birds, and the endangered swamp partridge and Bengal florican. The Koshi Barrage is an important resting place of migratory birds, including 87 winter and trans-Himalayan migratory species.