If something is sacred ... do you pollute it?!?

The river Ganges is considered sacred and is personified as the goddess Gaṅgā. She is worshiped by Hindus who believe that bathing in the river causes the remission of sins and facilitates Moksha (liberation from the cycle of life and death), and that the water of the Ganges is considered very pure.

So why is it one of the most polluted rivers in the world?
Do they believe Ganga will magically remove the pollution, or bless it somehow?
Or maybe they're trying to give everybody superpowers, via toxic waste (like in comics)?

Or is it just another example of the difference between what people say they believe, and how they actually live their lives?