PURPORT

Here we understand that the Ganges began when the water from Lord Brahma's kamandalu washed the lotus feet of Lord Vamanadeva. But in the Fifth Canto it is stated that the Ganges began when Vamanadeva's left foot pierced the covering of the universe so that the transcendental water of the Causal Ocean leaked through. And elsewhere it is also stated that Lord Narayana appeared as the water of the Ganges. The water of the Ganges, therefore, is a combination of three transcendental waters, and thus the Ganges is able to purify the three worlds. This is the description given by Srila Visvanatha Cakravarti Thakura.