Hundreds of millions of people live along the river banks of the Ganges, and many depend on it for their livelihoods. To Hindus, the Ganges is a holy river - attracting huge numbers of pilgrims. But it is also amongst the world's most polluted waterways. As India grows economically, lifestyles and livelihoods that have existed for centuries are being disrupted, as our reporter finds in Varanasi.