The Hindu Kush form the boundary between the Indus watershed in South Asia, and Amu Darya watershed in Central Asia. Melt water from snow and ice feeds major river systems in Central Asia: the Amu Darya, Helmand River (which is a major source of water for the Sistan Basin in southern Afghanistan and Iran), and the Kabul River - the last of which is a major tributary of the Indus River. Smaller rivers with headwaters in the range include them Khash, the Farah and the Arashkan (Harut) rivers. The basins of these rivers serves the ecology and economy of the region, but the water flow in these rivers greatly fluctuate, and reliance on these has been a historical problem with extended droughts being commonplace. The eastern end of the range, with the highest peaks, high snow accumulation allows to long-term water storage.