In the ancient days the annual festival of Tirunavay the temple here is dedicated to Mahavishnu-was celebrated for one month, from the Puyam or eighth asterism in the solar month Makaram (January-February) to the Makam or tenth asterism in the following month of Kumbha (February - March). Once in twelve years the festival is known as Mahamagha or Mamamkam which was held very sacred because of the arattu or immersion of the Lord's image in the river, Bharatapuzha on the Makam day.
It was believed that the waters of the holy Ganges flew into the river on this occasion and hence people from the most distant parts of Kerala used to come to Tirunavay for the festival. It is not known when this festival was instituted. The Cheraman rulers of Kodungallur celebrated it at first. After their disappearance the Vallatri took their place as its Rakshapurusha or protector. The Zamorin with a view to securing for himself the time-honoured privilege of presiding over Mamamkam ousted the Vallatri in the 14th century. The last Mamamkam was celebrated in 1766. The festival was to Kerala what the Olympian and Pythian festivals had been too ancient Greece.