Ganga in Hinduism

Birth

There are several Hindu beliefs that give various versions of the birth of Ganga. According to one version, the sacred water in Brahma's Kamandalu (water-vessel) became personified as a maiden, Ganga. According to another (Vaishnavite) legend, Brahma had reverently washed the feet of Vishnu and collected this water in his Kamandalu. According to yet a third version, Ganga was the daughter of Himavan, king of the mountains, and his consort Mena; she was thus a sister of the goddess Parvati. Every version declares that she was raised in the heavens, under the tutelage of Brahma

Descent to earth

Several years later, a king named Sagara magically acquired sixty thousand sons. One day, King Sagar performed a ritual of worship for the good of the kingdom]. One of the integral parts of the ritual was a horse, which was stolen by the jealous Indra. Sagara sent all his sons all over the earth to search for the horse. They found it in the nether-world (or Underworld) next to a meditating sage Kapila. Believing that the sage had stolen the horse, they hurled insults at him and caused his penance to be disturbed. The sage opened his eyes for the first time in several years, and looked at the sons of Sagara. With this glance, all sixty thousand were burnt to death.[1]
The souls of the sons of Sagara wandered as ghosts since their final rites had not been performed. When Bhagiratha, one of the descendants of Sagara, son of Dilip, learnt of this fate, he vowed to bring Ganga down to Earth so that her waters could cleanse their souls and release them to heaven.
Bhagiratha prayed to Brahma that Ganga come down to Earth. Brahma agreed, and he ordered Ganga to go down to the Earth and then on to the nether regions so that the souls of Bhagiratha's ancestors would be able to go to heaven. Ganga felt that this was insulting and decided to sweep the whole earth away as she fell from the heavens. Alarmed, Bhagiratha prayed to Shiva that he break up Ganga's descent.
Ganga arrogantly fell on Shiva's head. But Shiva calmly trapped her in his hair and let her out in small streams. The touch of Shiva further sanctified Ganga. As Ganga travelled to the nether-worlds, she created a different stream to remain on Earth to help purify unfortunate souls there. She is the only river to follow from all the three worlds - Swarga (heaven), Prithvi (earth) and, Patala (neitherworld or hell). Thus is called "Tripathagā" ( one who travels the three worlds) in Sanskrit language.
Because of Bhagiratha's efforts Ganga descended on to earth and hence the river is also known as Bhagirathi, and the term "Bhagirath prayatna" is used to describe valiant efforts or difficult achievements.
Another name that Ganga is known by is Jahnavi. Story has it that once Ganga came down to earth, on her way to Bhagiratha, her rushing waters created turbulence and destroyed the fields and the sadhana of a sage called Jahnu. He was angered by this and drank up all of Ganga's waters. Upon this, the Gods prayed to Jahnu to release Ganga so that she could proceed on her mission. Pleased with their prayers, Jahnu released Ganga (her waters) from his ears. Hence the name "Jahnavi" (daughter of Jahnu) for Ganga.

It is sometime believed that the river will finally dry up at the end of Kali Yuga (the era of darkness, the current era) just as with the Sarasvati river, and this era will end. Next in (cyclic) order will be the Satya Yuga or the era of Truth.