Srimad-Bhagavatam: Canto 5 - Chapter 1 - Verse 1
श्रीशुक उवाचतत्र भगवत: साक्षाद्यज्ञलिङ्गस्य विष्णोर्विक्रमतो वामपादाङ्गुष्ठनखनिर्भिन्नोर्ध्वाण्डकटाहविवरेणान्त:प्रविष्टा या बाह्यजलधारा तच्चरणपङ्कजावनेजनारुणकिञ्जल्कोपरञ्जिताखिलजगदघमलापहोपस्पर्शनामला साक्षाद्भगवत्पदीत्यनुपलक्षितवचोऽभिधीयमानातिमहता कालेन युगसहस्रोपलक्षणेन दिवो मूर्धन्यवततार यत्तद्विष्णुपदमाहु: ॥ १ ॥
śrī-śuka uvācatatra bhagavataḥ sākṣād yajña-liṅgasya viṣṇor vikramato vāma-pādāṅguṣṭha-nakha-nirbhinnordhvāṇḍa-kaṭāha-vivareṇāntaḥ-praviṣṭā yā bāhya-jala-dhārā tac-caraṇa-paṅkajāvanejanāruṇa-kiñjalkoparañjitākhila-jagad-agha-malāpahopasparśanāmalā sākṣād bhagavat-padīty anupalakṣita-vaco ’bhidhīyamānāti-mahatā kālena yuga-sahasropalakṣaṇena divo mūrdhany avatatāra yat tad viṣṇu-padam āhuḥ.
Śukadeva Gosvāmī said: My dear King, Lord Viṣṇu, the enjoyer of all sacrifices, appeared as Vāmanadeva in the sacrificial arena of Bali Mahārāja. 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 Viṣṇupadī. Later she received other names like Jāhnavī and Bhāgīrathī. 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 Viṣṇupada [“situated on Lord Viṣṇu’s lotus feet”].
In this verse, Śukadeva Gosvāmī describes the glories of the Ganges River. The water of the Ganges is called patita-pāvanī, 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 Śaṅkarācārya, have composed prayers in praise of the Ganges, and the land of India itself has become glorious because such rivers as the Ganges, Yamunā, Godāvarī, Kāverī, Kṛṣṇā and Narmadā flow there. Anyone living on the land adjacent to these rivers is naturally advanced in spiritual consciousness. Śrīla Madhvācārya says: Standing on His right foot and extending His left to the edge of the universe, Lord Vāmana became known as Trivikrama, the incarnation who performed three heroic deeds.