The preponderance of religious bathing festivals in India is really confusing. The Wall Street Journal Photo Journal featured the above photograph of a Hindu holy man drying his clothes after a ritualistic bath in the River Ganges during the annual Magh Mela in Allahabad. However, the Ardh Kumbh is also being held in Haridwar from January 14 to April 28, 2010...so there are two overlapping religious festivals with the same rituals.
Magh Mela is observed during Magh and Falgun months (Hindu calendar) for nearly 45 days, and this year ends on February 12, 2010. The ritual of bathing at the Prayag Sangam in Allahabad has a great significance, and attracts millions of devotees to the confluence of rivers Ganges, Yamuna and the mythical Saraswati.
It is believed that bathing in sacred rivers during these festivals breaks the circle of life & death, and liberates Hindus to attain moksha.
Personally, I'd much rather attend the Magh Mela over the Haridwar Ardh Kumbh. Of course, neither can come close to what I experienced during the 2001 Maha Kumbh Mela in Allahabad, but Haridwar (despite the relative proximity of Rishikesh) is a pretty awful town, hence my bias.