As millions of Hindus prepare to descend on the holy city of Haridwar, the authorities have urged people to avoid dirtying the Ganges - India's most sacred river yet one of its most heavily polluted.
When the three-month-long Kumbh Mela festival begins tomorrow in the northern Indian city, 2.5 millionpeople could take a ritual bath in the river on the first day alone.
Many more - perhaps as many as 60 million - will follow in the weeks ahead.
Yet for all its importance to the Hindu faith, those overseeing the festival - held in four different locations over a period of 12 years - are aware of the very damaging effect so many people could have on the river that is considered a living Goddess.
Yesterday, the government of Uttarakhand state took out full-page advertisements in national news papers listing a code of conduct for pilgrims.
Chief among the rules is not to use detergents or soaps when bathing in the river, and not to bring polythene and plastic.
"Observe the sanctity of the holy sites," it adds. Along with several other sacred rivers, the state of the Ganges is one of India's greatest environmental embarrassments.
A combination of billions of litres of raw sewage being pumped into the river along with the waste from industry have transformed the 1,500-mile waterway into one of the world's most heavily polluted.
Just last month, the World Bank announced it was to give India US$1bn to help it clean up the river, which provides a lifeline to at least 400 million people who either live beside it or depend on it to irrigate their crops.
"There is an increasing pressure from population at these festivals," said Lalit Pande, director of the Uttarakhand Environmental Education Centre.
"But most of the problems with the pollution comes from sewage that is discharged."
