A pilgrimage to heavenly cleansing, visible from heaven Billed as the biggest gathering on Earth, India's Maha or Great Kumbh Mela is expected to draw up to 100 million pilgrims to bathe in holy waters at the confluence of the Ganges and Yamuna rivers. The belief that ritualistic bathing will cleanse sins - in some of the most polluted and contaminated rivers in the world - is all part of the massive 55-day religious festival that takes place every 12 years in Allahabad, northern India. Other activities include religious discussions, devotional singing, and mass feeding of holy men and women and the poor. The event concludes on March 10. It is the most sacred of pilgrimages for Hindus and dates back at least 1,000 years. Crowds: The previous festival in January, 2001, attracted more than 30 million people and the crowds of orange-robed bathers were visible from space. In satellite images prior to the festival, the Ganges appears muddy and pale yellow and the Yamuna was green. During the gathering, the vast number of bathers appeared to turn the water a reddish-brown. Housing:This year, the vast number of participants have transformed the mudflats around the delta into a teeming tent city. Organizers have arranged for 35,000 toilets, 80 million litres of drinking water, 243 doctors and 30,000 police for the occasion, according to the BBC. Health:According to National Geographic, there are a variety of health issues related to water quality. Urinary infections are one of the more persistent problems of this year's festival because of poor water quality of the Ganges. Four to five cases a day have been treated at Kumbh's central hospital. Women'srights: For the first time, women ascetics from the elite Hindu Naga holy order have won the right to have their own separate camp at the Kumbh Mela, according to the BBC. Unlike most of the monks who enter the waters naked, the women are wrapped in a single piece of unstitched cloth. Foreigners:Officials say as many as 10,000 foreigners from the United States, France, Britain Germany, Italy and Switzerland are taking part in the festival, according to the Times of India. Celebrity factor:Bollywood celebrities have been urged to stay away from the festival on high interest days, according to leading entertainment website Bollywood Hungama. Authorities reportedly fear a stampede if the stars promote their upcoming films by mingling with the congregation.