SB 5.17.1

śrī-śuka uvāca
tatra 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.
Synonyms: 
śrī-śukaḥ uvāca — Śrī Śukadeva Gosvāmī said; tatra — at that time; bhagavataḥ — of the incarnation of the Supreme Personality of Godhead; sākṣāt — directly; yajña-liṅgasya — the enjoyer of the results of all sacrifices; viṣṇoḥ — of Lord Viṣṇu; vikramataḥ — while taking His second step; vāma-pāda — of His left leg; aṅguṣṭha — of the big toe; nakha — by the nail; nirbhinna — pierced; ūrdhva — upper; aṇḍa-kaṭāha — — the covering of the universe (consisting of seven layers — earth, water, fire, etc); vivareṇa — through the hole; antaḥ-praviṣṭā — having entered the universe; — which; bāhya-jala-dhārā — the flow of water from the Causal Ocean outside the universe; tat — of Him; caraṇa-paṅkaja — of the lotus feet; avanejana — by the washing; aruṇa-kiñjalka — by reddish powder; uparañjitā — being colored; akhila-jagat — of the whole world; agha-mala — the sinful activities; apahā — destroys; upasparśana — the touching of which; amalā — completely pure; sākṣāt — directly; bhagavat-padī — emanating from the lotus feet of the Supreme Personality of Godhead; iti — thus; anupalakṣita — described; vacaḥ — by the name; abhidhīyamānā — being called; ati-mahatā kālena — after a long time; yuga-sahasra-upalakṣaṇena — consisting of one thousand millenniums; divaḥ — of the sky; mūrdhani — on the head (Dhruvaloka); avatatāra — descended; yat — which; tat — that; viṣṇu-padam — the lotus feet of Lord Viṣṇu; āhuḥ — they call.
Translation: 
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”].
Purport: 

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:

vārāhe vāma-pādaṁ tu
 tad-anyeṣu tu dakṣiṇam
pādaṁ kalpeṣu bhagavān
 ujjahāra trivikramaḥ

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.