Gangotri is the origin of the river Ganga and is one of the four sites in the Char Dham pilgrimage circuit.
The river is called Bhagirathi at the source and acquires the name Ganga (the Ganges) from Devprayag onwards where it meets the Alaknanda.
Information about Bhavishya Badri Temple is also available in this page.
Web : http://en.wikipedia.org/wiki/Gangotri