Koshi Tappu Wildlife Reserveकोशी टप्पु वन्यजन्तु आरक्ष

Koshi Tappu, established in 1976, is the only wildlife reserve left in Nepal's protected-area system. Strung along the Sapta Koshi floodplain across Sunsari, Saptari and Udayapur, it sits at just 75–81 m — the lowest protected area in the country — over 176 km² of marsh, mudflat and tall grassland that floods and shifts with the great river.

The reserve was created specifically to save Nepal's last wild water buffalo (arna, Bubalus arnee), a herd that has grown from around 150 to 432 by 2016. It also shelters the Gangetic river dolphin and is, above all, a world-class wetland for birds: 485 species have been recorded, including the Bengal florican, vast flocks of ducks and waterfowl, and migrants on the Central Asian Flyway, alongside some 200 fish species.

On 17 December 1987 Koshi Tappu became Nepal's first Ramsar Wetland of International Importance (around 17,500 ha), launching the country's wetland-conservation era. Today it is Nepal's top birdwatching destination and the stronghold of the arna it was built to protect.