A million Hindus plunged into the freezing waters of the holy Ganges River Monday, marking the beginning of the world's largest religious festival.

The Kumbh Mela festival, held every 12 years in the Indian town of Allahabad, will see up to 100 million worshippers gather over the next 55 days to take a ritual bath in the Ganges, whose waters are believed to cleanse sins and bestow blessings.

According to Hindu mythology, the Kumbh Mela celebrates the victory of gods over demons in a battle over a nectar that would bestow immortality.

Drops of the nectar of immortality are said to have fallen during the battle on Allahabad, Nasik, Ujjain and Haridwar. The Kumbh Mela is held periodically in all the towns.

Organizing and managing the onslaught of so many people is a massive undertaking. To cope with the flow of people, authorities in the state of Uttar Pradesh have installed thousand of toilets, laid hundreds of kilometers of water pipes and roads, and deployed thousands of police.

Despite its importance in Hinduism, the Ganges is tainted by industry and the settlements along its banks, which quickly turn the clear waters from the Himalayas into a murky, frothy brown downstream.