Koshi Tappu Wildlife Reserve was mainly established to protect the rare wild buffaloes (Arnas) in 1976, which was declared as the Ramsar site in 1987. The park with an area of 175 sq km is mostly a wet land, which is defined by the eastern and western embankments of the Sapta Koshi river in Sunsari and Saptari districts. The area of the reserve extends to the north of one kilometer long barrage that spans the Koshi river. The outstanding wetland, that is created from the vast expanse of flood water by barrage makes home to marshes, lagoons and mudflats.

The vegetation mainly includes tall khar-pater grasslands with a few patches of khair-sissoo scrub forest and deciduous mixed riverine forest, which offers an important habitat for a variety of wildlives such as hog deer, spotted deer, wild boar and blue bull (Nilgai). The grasslands support an important population of the Asiatic wild buffaloes or Arnas (the last surviving population was 100).

The park is well known as the bird watching paradise. It is one of the finest bird watching sanctuaries in Asia. Espesially in the winter season (October to March) the barrage acts as the most important resting place for migratory birds. A total of 280 different species of birds have been recorded in the reserve. The endangered Gharial crocodile and Gangetic dolphin also have been recorded in the Koshi River.

The other main tourist attraction of the reserve is the nature walk that offers a life time memories to those who are curious to explore the preservance of the grassland, woodland and vicinity of the barrage, including the river lagoons. The wild life reserve also serves as an ideal location for those who wants to have a break in their journey to have a brief relaxing stay while en-route to Sikkim, Darjeeling and Bhutan as well as the trekkers and mountaineers who are returning from Arun Valley, Kanchanjunga and Makalu region.

Best time:
The winter season (October to March). Since the weather is clear Mt Makalu (5th highest peak) and several other mountain peaks are visible, and this is the perfect time for the migratory birds to come have rest in the reserve.