Ganga is unable to sustain the only population of freshwater dolphins found in the country.
The survival of the Ganges River dolphin is threatened by:
(a) accidental killing through entanglement in fishing gear, most often nylon gill nets;
(b) directed harvest, generally for dolphin oil used as a fish attractant and for medicinal purposes;
(c) water development projects (e.g. water extraction and the construction of barrages, high dams, and embankments);
(d) increasing levels of chemical pollution, such as from industrial discharges and the use of pesticides;
(e) increasing levels of other forms of pollution, such as municipal sewage discharge and noise from vessel traffic; and
(f) overexploitation of prey, mainly due to the widespread use of non-selective fishing gear during fish breeding migrations and early juvenile growth.
Construction of at least 50 dams within the known or suspected historic range of the Ganges River dolphin has dramatically affected its habitat, abundance and population structure. Dam construction and operation cause major changes in the flow regime, sediment load, and water quality of rivers. Dams eliminate many of the dynamic attributes of downstream waters and block the flow-through of sediment essential to the formation of islands and sandbars. Downstream flows are normally not allowed to overspill riverbanks onto adjacent floodplains. As a result, fish production decreases dramatically. Natural fluctuations in flow, temperature, and detritus loading, which provide optimal conditions for a large number of aquatic organisms, are suppressed by dams, and the number of ecological niches available for supporting diverse communities of riverine biota is reduced.