14th January 2013 is the day of Makar Sankranti, which is a harvest festival just like Lohri. Incidentally it falls on this day every year. This is perhaps because it is calculated as per Solar Cycle which is the basis of Christian Calender as well. Astronomically it means that Sun has moved to Capricorn Zodiac. Makar means Capricorn and Sankrant means movement in which two zodiacs of Capricorn and Cancer shall be joined by Sun for a moment, while passing through the one to another. Every 12 years, on this day, largest congregation of human kind takes place on river banks of rivers Ganga (British called her Ganges) (her because she is a goddess) and Godawari at four places. Allahabad is the most prominent place for Kumbh as the Maha Kumbh (Great Kumbh) after every 144th years takes place here alone. Allahabad is intersection (called Sangam which means amalgamation) of three rivers namely Ganga, Yamuna & Saraswati. On this occasion people take a holy dip in the waters of Ganga and purify themselves from their past sins This bathing is considered holy according to Hindu Mythology.
According to Mr. Jairam Ramesh the then, Minister for sanitation and drinking water:
Rivers are not rivers in India. Rivers have become sewers. The 500-km stretch of Ganga between Kannuaj and Varanasi is just sewer.