Much of the river's pollution comes from untreated industrial waste and city sewage, which is a policy problem not a social one.How about not polluting it in the first place? This requires a huge shift in society and culture. Impossible in the short term. Might take 100 years of education to return toxicity levels to a safe threshold.
This problem only gets worse given the innumerable tributaries Ganges has which means cleaning the Ganges means cleaning the entire river system which includes huge tributaries like Yamuna, Ghaghra etc.
Common people don't pollute the river knowingly, instead they do so because they have got no other choice.
Cleaning the Ganges is a herculean task and I would be pleasantly surprised if we manage to pull this off, for me it would be the most impressive feat of modern India