India's greatest river, the mighty Ganges, is one of the world's dirtiest. The river's revered by Hindus - but it is also the sewer that carries away the waste from 450 million people. Hundreds of millions of people depend on the river, yet pollution from industry, agriculture - even religious waste - has turned its sacred waters into a toxic and deadly cocktail. The Indian prime minister has staked his political reputation on cleaning it up, but can the Ganges be saved?