The three largest rivers in South Asia are -Indus River (3200km long). This flows through Pakistan, India and China. 93%, 5% and 2% respectively in each country. The main sources of this are the SĂȘnggĂȘ River, Tibetan Plateau and the Gar Rifer -Brahmaputra River (2900km long). This flows through China, India and Bangladesh. The main source of this is from the Himalayas. -Ganges River (2525km long). This flows through India and Bangladesh. The main sources of the Ganges are the Satopanth Glacier and the Gangotri Glacier, and the water from some of their peaks, such as Trisul, Nando Kot, Nanda Devi, Kedarnath and Kamet. Hope this helps