Purity of River Ganges

Srimad Bhagavatam 4.1.14: My dear Vidura, of the two sons, Kaśyapa and Pūrṇimā, Pūrṇimā begot three children, namely Viraja, Viśvaga and Devakulyā. Of these three, Devakulyā was the water which washed the lotus feet of the Personality of Godhead, Hari, and which later on transformed into the Ganges of the heavenly planets.

PURPORT

lt is also understood herein that Devakulyā is the presiding deity of the River Ganges, which comes down from the heavenly planets to this planet and is accepted to be sanctified because it touched the lotus feet of the Supreme Personality of Godhead, Hari.