The river's story is a descent. King Sagara's sixty thousand sons were burned to ash by a sage's anger, and their funeral rites could not be completed because no water on earth was pure enough; generations later Bhagiratha performed austerities until Ganga agreed to come down from heaven, and Shiva stood beneath to receive her in his matted hair, releasing her in streams so that the impact would not shatter the world. She flowed over the ashes and the dead were released. That is why the river is called Bhagirathi in its upper course, and why the story is told at the ghats where ashes are still immersed.
Ganga is worshipped as a goddess with her own iconography, riding a makara, and she is also a category. A tirtha is a crossing place, a ford between this world and the next, and the great tirthas of India are overwhelmingly on water. Diana Eck's study of Indian sacred geography follows how the whole network works: the Ganges is invoked into other rivers, into temple tanks, and into the pot of water used in a rite a thousand miles away, so that the presence of this river is portable in a way its water is not.
Seven rivers are named together in the standard invocation of the bathing rite, the Ganges first among them, and the confluence at Prayag where the Ganges meets the Yamuna and the invisible Sarasvati is the most powerful of all the crossings.