Ganga and Kali
Goddess Kali was very dark. Once she was in the company of beautiful, lovely, and fair complexioned heavenly nymphs and Lord Shiva jested about her dark complexity. Kali felt insulted and became very distracted at Shiva's remarks. She practiced punishment for one hundred years in the Himalayas and Shiva was forced to come and placate her anger. Kali asked the boon of having a fair complexion and Shiva directed her to have a bath in the heavenly Ganga. Kali took a bath in the river Ganga, and became as fair as lighting. From then onwards, Kali came to be known as Vidyut-Gauri.
Ganga is destined to flow on earth
It is said that during the struggle between the gods and the demons for ultimate supremacy, the demons had an advantage by hiding in the oceans of the earth during day and coming out to attack only during the night, when they were naturally more powerful. This frustrated the efforts of the gods and so they requested sage Agastya to solve their problem. The reowned sage Agastya, with the power of his asceticism, drank up the oceans of the earth and then the demons had no place to hide during the daytime. A fierce battle took place between the gods and the demons and finally the gods won the battle. Afterwards, they requested sage Agastya to release the ocean waters, but he was unable to do so, as he had digested it. Perplexed, the gods approached Lord Vishnu, who told them that the earth will soon receive the heavenly Ganga, as she was destined to come to earth and flow over the ashes of the sixty thousand sons of King Sagara, thereby liberating their souls.