Mother Ganga promised that she would enter all the rivers, lakes, ponds, wells, and all the streams on This Karthik Purnima Day. Our scriptures extolled the holiness of the Ganges. How safe is it to take a dip in the river knowing it is dirty and polluted with many dead bodies? 
In 1896 Ernest Hankin conducted research and proved that some kind of protective viruses develops and eat the bacteria that cause diseases. Mark Twain met Ernest Hankin and found out that certain viruses germinate in the Ganges and eat up the bacteria. In six hours, the water becomes pure and holy. Bacteria disappears. 

Even recent research in 2016 comes to the same conclusion. Ganga water is pure and holy. Take a dip. Happy Karthik Masa  Purnima.

https://www.youtube.com/watch?v=mWRjZEaMfWg