Devprayag is a Hindu holy city in India, where the Alaknanda and Bhagirathi rivers meet and become the Ganges river.
There is a Ghat (steps to the holy bath) at the Sangam, i.e. the exact point of the confluence. Hindu pilgrims take a holy dip right where the two sacred rivers meet.
In Hindu mythology and culture, the Bhagirathi (on the left, with the green water) is considered the source stream of the Ganges. However, in hydrology, the other headstream, Alaknanda (on the right, with the brown water), is considered the source stream on account of its great length and discharge.
For more info about this place, go to en.wikipedia.org/wiki/Devprayag.