This 175 square kn reserve is located in the Terai lowlands where vegetation is mainly wetland grassland, scrub and deciduous forests. The reserve is unique for its wild arna buffaloes although it also hosts hog deer, wild boar, spotted deer and blue bulls. There are over 350 species of birds including ibeses, storks, egrets, herons, swamp partridges and Bengal floricians. In the Koshi River, endangered gharials, marsh crocodiles and Gangetic dolphins have been observed.

Activities include game viewing and bird watching. Accommodation is available at tented camps.

To get to Koshi Tappu takes a one hour drive from Biratnagar which is 50 minutes by air or 541 km by road from Kathmandu

The best time to visit is between October and March or when it's hotter between April and June. The rainy season lasts between July and September.