Despite their scale, the Himalayas do not form a major watershed, and a number of rivers cut through the range, particularly in the eastern part of the range. As a result, the main ridge of the Himalayas is not clearly defined, and mountain passes are not as significant for traversing the range as with other mountain ranges. The rivers of the Himalayas drain into two large river systems:
- The western rivers combine into the Indus Basin. The Indus itself forms the northern and western boundaries of the Himalayas. It begins in Tibet at the confluence of Sengge and Gar rivers and flows north-west through India into Pakistan before turning south-west to the Arabian Sea. It is fed by several major tributaries draining the southern slopes of the Himalayas, including the Jhelum, Chenab, Ravi, Beas and Sutlej rivers, the five rivers of the Punjab.
- The other Himalayan rivers drain the Ganges-Brahmaputra Basin. Its main rivers are the Ganges, the Brahmaputra and the Yamuna, as well as other tributaries. The Brahmaputra originates as the Yarlung Tsangpo River in western Tibet, and flows east through Tibet and west through the plains of Assam. The Ganges and the Brahmaputra meet in Bangladesh and drain into the Bay of Bengal through the world's largest river delta,