Ganga is the longest river of India. The total length of the Ganga river from its source to its mouth (measured along the Hughli) is 2525 km of which 1450 km is in the Uttar Pradesh, 445 km in Bihar and 520 km in West Bengal. The remaining 110 km stretch of the Ganga forms the boundary between Uttar Pradesh and Bihar.
The Ganga originates as Bhagirathi from the Gangotri glacier in Uttar
Kashi District. It is joined by the Alaknanda at Devaprayag and the
combined flow of the Bhagirathi and the Alaknanda is known as Ganga.
After traveling 280 km from its source, Ganga enters plains at Haridwar.
At Allahabad, about 770 km south-east of Haridwar, Ganga is joined by
Yamuna, which is its most important tributary. After Farraka in West
Bengal, the river ceases to be known as the Ganga. It bifurcates itself
into Bhagirathi-Hughli in West Bengal and Padma-Meghna in Bangladesh.
After traversing 220 km further down in Bangladesh, the Brahmaputra
joins it at Goalundo and after meeting Meghna 100 km downstream the
Ganga joins the Bay of Bengal.