Gangaa is the daughter of Brahmaa Jee, who came out of Vishnu's big toe's nail when Brahmaa Jee washed His foot when Bhagavaan measured the Swarg Lok in His second foot. It is when Raajaa Bali was doing a Yagya to become very powerful - after the completion of that Yagya he could not be defeated. So Bhagavaan took Avataar in Kashyap and Aditi's house as Vaaman Avataar and asked for three feet land from Bali in alms. Raajaa Bali promised Him to give this much land.

His Guru Shukraachaarya Jee warned him that, that child was not a small child but He was Bhagvaan Himself, but once promised Bali did not break it saying, "First, nobody goes empty-handed from my door whosoever he is; second, I have already promised Him to give whatever he asks for, so I have to give Him whatever He wants; third, it is a great privilege for me that Bhagvaan Himself has come to ask for anything from me, if at all He is Bhagvaan. So considering all the three reasons I cannot go back from my promise."

So Bali gave Him permission to measure three steps land Himself. That Braahman boy grew up His body so large that His head started touching the sky. In one step He measured Prithvi Lok, in second step He measured Swarg Lok, and with His body He covered the wbhole sky. When His foot reached Swarg Lok, then Brahmaa Jee and other Devtaa worshipped it from his Kamandal water. At that time the water came out of Brahmaa Jee's Kamandal to wash Vishnu's foot it converted into Gangaa River and blessed Dev Lok with her holy water.

Later Bhageerath Jee brought her on Prithvi to give Mukti to his 60,000 great-grandfathers.