Abstract: The river Ganga (~2500 km long) originates from the Gangotri glacier in the central Himalayas and drains into the Bay of Bengal. The river covers a drainage basin area of 1.08×106 km2 and provides water for agricultural, domestic and industrial use. The climate over the Ganga river basin varies widely from tropical/subtropical in the south to the areas with sub-zero mean annual temperatures in the high Himalayas. The flow of water in the Ganga not only depends on glacier melt but also contribution from surface runoff captured from snow-melt and rainwater within the catchment area and groundwater. The vulnerability of different water reservoirs to natural and anthropogenic changes can affect the future flow as well as the nutrient dynamics of the Ganga river. Therefore, it is crucial to monitor and quantify the contribution of water from different sources into the river Ganga. In this talk, I shall discuss with the help of isotopic data, the impact of climate and anthropogenic activities in the river Ganga.