Mahamaham, also known as Mahamagham or Mamangam, is a Hindu festival celebrated every 12 years in the Mahamaham tank located in the city of Kumbakonam in Tamil Nadu in the south of India. This 20-acre square tank surrounded by Shiva mandapams is believed by Tamil Hindus to be ancient, and the holy confluence of nine Indian river goddesses: Ganga, Yamuna, Sarasvati, Narmada, Godavari, Krishna, Tungabhadra, Kaveri, and Sarayu, states Diana Eck – a professor of Comparative Religion and Indian Studies. On the day of the Mahamaham festival, the river goddesses and Shiva gather here to rejuvenate their waters, according to a legend in the Periya Purana. The Hindus consider taking a pilgrimage and holy dip at the Mahamaham tirtha on the day of Mahamaham festival as sacred. The event attracts chariot processions, street fairs and classical dance performances in temple mandapas. The 12-year cycle Mahamaham festival in Tamil Nadu is observed in the Hindu calendar month of Magha, and is a symbolic equivalent of the Kumbh Mela.

Mahamaham tank is a huge temple tank located in Kumbakonam, Tamil Nadu, India. It is considered to be the foremost and one of the largest temple tanks in Tamil Nadu. The Masimaham festival held in the tank has 100,000 visitors and the once-in-12-year Mahamaham festival has close to 2 million visitors.