This pic is from Kumbh(Pot) Mela(Fair), a festival and pilgrimage occurs four times every twelve years, once at each of the four locations in India. Attended by millions of people, making it the largest pilgrimage gathering around the world and unique in many ways.
A ritual bath at a predetermined time and place is the major event of this festival. Thousands of holy men/women (monks, saints, naga sadhus) grace the occasion by their presence. A holy dip in the river is considered to wash away all your past sins. Other activities include religious discussions, devotional singing, mass feeding of holy men/women and the poor, and religious assemblies where doctrines are debated and standardized.
The Four locations where kumbh mela occurs are Prayag (near the city of Allahabad, in the state of Uttar Pradesh) at the confluence of three rivers Ganga (Ganges), Yamuna and Saraswati
Haridwar (in the state of Uttar Pradesh) where the river Ganga enters the plains from Himalayas
Ujjain (in Madhya Pradesh), on the banks of Ksipra river
Nasik (in Maharashtra) on the banks of Godavari river.