The river Ganges is very sacred to the Hindus. Those who take a dip in the river are said to be ridden of all their sins and attain immortality.
It is believed that the river used to flow in the heavens till the sage, Bhageerath, made severe penances and directed its flow towards the earth to save his 60000 ancestors who were lying in the nether world (patala) in a heap of ashes due to a curse delivered by sage Kapila.
Since earth was not yet prepared to withstand the impact of its downward descent, Lord Siva came forward to allow it to fall on His head first and then flow down towards the earth. He also made the Ganges His permanent companion. Three of them flowed west and three east. The remaining seventh stream followed Bhageerath to the nether worlds and helped all his ancestors from damnation. The river is eternal and said to reward immortality to those who come into contact with it.
Symbolically, on the earth plane, the river stands for divine consciousness. It descended into the earth consciousness through the efforts of sage Bhageerath.
Being divine consciousness, who ever immerses himself in it becomes immortal. It is eternal because it is the highest consciousness, which human beings are capable of attaining during their spiritual endeavor.
In the body plane, the story of Ganga reveals the divine origin of kundalini and its descent through the various chakras of the body into the lowest chakra, the muladhara corresponding to the patala regions of the world, where it remains coiled like a serpent till it ascends again into the higher chakras during ones spiritual sadhana.
If we interpret the word Bhageerath as “bhaga”+”rathi” it means he who rides bhaga (the reproductive organ) which is the place where the kundalini ordinarily remains in a coiled state. Probably the sons of Sagara whom sage Bhagirath rescued correspond to the various nerve centers in that region.
The divine consciousness thus entering into earth plane (human body) through Lord Siva made spiritual evolution possible on earth as well in human body.
The second interpretation is that Ganga symbolically represents a particular branch of divine and esoteric knowledge with the powers to elevate the dead as well as the living towards heavens, with the strength of its purity and illumination, which was probably not available to the mankind, till sage Bhagirath tried to bring it down into human awareness through his devotion and surrender to Lord Siva, who ultimately helped him to receive it and help his ancestors attain immortality.