The Ganga is the longest river in India, stretching 2,525 km from its source to its mouth. It flows 1,450 km through Uttar Pradesh, 445 km through Bihar, and 520 km in West Bengal, with 110 km forming the boundary between Uttar Pradesh and Bihar. Originating as the Bhagirathi from the Gangotri glacier in Uttarkashi, it merges with the Alaknanda at Devprayag to officially become the Ganga. It enters the plains at Haridwar after traveling 280 km from its Himalayan source.

At Allahabad (Prayagraj), 770 km from Haridwar, the Ganga is joined by its major tributary, the Yamuna. After Farraka in West Bengal, it splits into two branches , the Bhagirathi-Hooghly flowing through India and the Padma-Meghna through Bangladesh. The Brahmaputra merges with the Ganga at Goalundo in Bangladesh, and after meeting the Meghna, the river finally drains into the Bay of Bengal, completing its journey.