Kṛṣṇa says in Bhagavad-gītā (BG 7.4):
- bhūmir āpo 'nalo vāyuḥ
- khaṁ mano buddhir eva ca
- ahaṅkāra itīyaṁ me
- bhinnā prakṛtir aṣṭadhā
"Earth, water, fire, air, ether, mind, intelligence and false ego—all together these eight comprise My separated material energies."
The energy of the Lord acts throughout the creation, just as heat and light, the energies of the sun, act within the universe and make everything work. The specific rivers mentioned in the śāstras are also energies of the Supreme Personality of Godhead, and people who regularly bathe in them are purified. It can actually be seen that many people are cured of diseases simply by bathing in the Ganges. Similarly, the inhabitants of Krauñcadvīpa purify themselves by bathing in the rivers there.