SB 5.17.1
sri-suka uvaca
tatra bhagavatah saksad yajña-lingasya visnor vikramato vama-padangustha-nakha-nirbhinnordhvanda-kataha-vivarenantah-pravista ya bahya-jala-dhara tac-carana-pankajavanejanaruna-kiñjalkoparañjitakhila-jagad-agha-malapahopasparsanamala saksad bhagavat-padity anupalaksita-vaco ’bhidhiyamanati-mahata kalena yuga-sahasropalaksanena divo murdhany avatatara yat tad visnu-padam ahuh.
Translation by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
Sukadeva Gosvami said: My dear King, Lord Visnu, the enjoyer of all sacrifices, appeared as Vamanadeva in the sacrificial arena of Bali Maharaja. Then He extended His left foot to the end of the universe and pierced a hole in its covering with the nail of His big toe. Through the hole, the pure water of the Causal Ocean entered this universe as the Ganges River. Having washed the lotus feet of the Lord, which are covered with reddish powder, the water of the Ganges acquired a very beautiful pink color. Every living being can immediately purify his mind of material contamination by touching the transcendental water of the Ganges, yet its waters remain ever pure. Because the Ganges directly touches the lotus feet of the Lord before descending within this universe, she is known as Visnupadi. Later she received other names like Jahnavi and Bhagirathi. After one thousand millenniums, the water of the Ganges descended to Dhruvaloka, the topmost planet in this universe. Therefore all learned sages and scholars proclaim Dhruvaloka to be Visnupada [“situated on Lord Visnu’s lotus feet”].
Purport by His Divine Grace A. C. Bhaktivedanta Swami Srila Prabhupada:
In this verse, Sukadeva Gosvami describes the glories of the Ganges River. The water of the Ganges is called patita-pavani, the deliverer of all sinful living beings. It is a proven fact that a person who regularly bathes in the Ganges is purified both externally and internally. Externally his body becomes immune to all kinds of disease, and internally he gradually develops a devotional attitude toward the Supreme Personality of Godhead. Throughout India, many thousands of people live on the banks of the Ganges, and by regularly bathing in her waters, they are undoubtedly being purified both spiritually and materially. Many sages, including Sankaracarya, have composed prayers in praise of the Ganges, and the land of India itself has become glorious because such rivers as the Ganges, Yamuna, Godavari, Kaveri, Krsna and Narmada flow there. Anyone living on the land adjacent to these rivers is naturally advanced in spiritual consciousness. Srila Madhvacarya says:
varahe vama-padam tu
tad-anyesu tu daksinam
padam kalpesu bhagavan
ujjahara trivikramah
Standing on His right foot and extending His left to the edge of the universe, Lord Vamana became known as Trivikrama, the incarnation who performed three heroic deeds.