The Ganga river rises from the Gangotri Glacier, at the height of 5163 metre, a part of Great Himalayas that lies in Uttarakhand. The river cuts through the Great Himalayas and the lesser Himalayas in narrow gorges. It is called Bhagirathi above Dev Prayag and Ganga below this town.
The Alaknanda, an important affluent, joins it at Dev Prayag.
At Haridwar, it leaves the Himalayas and enters the plain below this town. It runs towards the south-east up to Mirzapur and further down eastward in Bihar plain. It turns south-east near the Raj Mahal and after traversing same distance in Murshidabad district of West Bengal, it enters Bangladesh.
The total length of Ganga is about 2510 km.