The most sacred Hindu river, the Ganges, is suffering from depletion, pollution and has been the source of a long-running dispute between India and Bangladesh.
The glacier which feeds it is retreating hundreds of feet each year - experts blame climate change.
Deforestation in the Himalayas has caused subsoil streams flowing into the river to dry up.
Downstream, India controls the flow to Bangladesh with the Farakka Barrage, 10km on the Indian side of the border. Until the late 1990s, India used the barrage to divert the river to Calcutta to stop the city's port drying up during the dry season. This denied Bangladeshi farmers water and silt, and left the Sundarban wetlands and mangrove forests at the river's delta seriously threatened.
The two countries have now signed an agreement to share the water more equally. Water quality, however, remains a huge problem, with high levels of arsenic and untreated sewage in the river water.