Bardiya National Park and the Karnali river system hold a concentrated range of wildlife inside a single site. The Gangetic dolphin (Platanista gangetica), listed as endangered on the IUCN Red List, is the centrepiece: adults reach 2 to 2.6 m in length and navigate by echolocation because they are functionally blind. They surface every 30 to 90 seconds to breathe, which makes them visible from a low-profile river boat. Population counts for the Karnali and Geruwa segment are estimated in the range of 5 to 15 individuals; the wider Karnali system is considered one of Nepal's most important dolphin habitats.
Beyond the river, the park's grasslands and sal forest hold Bengal tiger, greater one-horned rhinoceros, Asian elephant, swamp deer (barasingha), spotted deer (chital), hog deer, wild boar and four-horned antelope. Mugger crocodile and gharial are regularly seen on sandbanks. Over 250 bird species use the riparian forest, grassland and wetland habitats, including Bengal florican (critically endangered), sarus crane, white-rumped vulture, peafowl and bar-headed geese. The Sonaha community on the river has coexisted with dolphins for generations and can offer additional context during the cultural visit on day 4.