The Karnali River, called Ghaghara River in India, Mapcha Tsangpo in Tibet, and the lower Ghaghara in Awadh called Sarayu River, is a perennial trans-boundary river that originates in the northern slopes of the Himalayas in the Tibetan Plateau, cuts through the Himalayas in Nepal and joins the Sharda River at Brahmaghat in India. Together they form the Ghaghara River, a major left-bank tributary of the Ganges. With a length of 507 km (315 mi), it is the longest river in Nepal. The total length of the Ghaghara up to its confluence with the Ganges at Revelganj in Bihar is 1,080 km (670 mi). It is the largest tributary of the Ganges by volume and the second largest by length after Yamuna.

Humla District, a part of Karnali Province, is one of the seventy-seven districts of Nepal. The district, with Simikot as its district headquarters, covers an area of 5,655 km2 (2,183 sq mi) and has population of 50,858 as per the census of 2011. Namkha is the largest rural municipal which lies in humla Humla is the 2nd largest district of Nepal. The southern and middle parts of Humla District are inhabited by Khas communities, originating from Sinja valley, whereas the higher and northern parts of Humla are mostly inhabited by culturally Tibetan communities.