Festivals are celebrated almost every month  and  of  those, the  Maham festival in the month of Masi ( February - March )  is important .  Once  in 12  years Mahamaham  Festival  is  celebrated  when  pilgrims from  far  and  wide  flock  to  the place  in  millions  and  take  bath  in the  Holy  Theertham,  the  Mahamaham  tank. The Amirtha Theertha which spilled from the pot stagnated in two places at Kumbakonam (KMU). One at the eastern side  and the other at the south western side of Kumbeswaran temple. The south western side tank is called Mahamaham tank while the eastern one is called as Porthamarai tank. (Pon - Gold , Thamarai - Lotus ).

Brahma thought that the right time to worship Shiva is during the month of Maasi ( second half of FEB. / first half of MAR. ). In this month ( when the moon is raising crescent and star - Ashwini ), he had a holy dip in Mahamaham tank and did Mahamaha Urchavam. On the tenth day he didurchava for Lord Kumbeswara in the tank. This is called Maham festival celebrated every year.

When Navakannigas ( Rivers - Ganga, Yamuna, Narmada, Saraswathi, Godavari,Cauvery, Sindhu, Sarayu, and Mahanadhi ) wanted to dispose the sins washed out by the people, and  prayed Shiva, the Lord asked them to take a holy dip during the auspicious time of  Mahmaham and purify themselves.

Auspicious time of Mahamaham
When Sun is in Kumbha rasi and Guru in Simha rasi on a full moon day, with Maham star in Rishibha Lagnam ( 10.30 - 12 Noon) , Mahamaham time falls.All the Gods in Kumbakonam are believed to come to the tank at that time.

Various Theerthams present in Mahamaham Tank
1. Vayu  2. Ganga 3. Brhama 4. Yamuna 5. Kubher 6. Godavari. 7. Eesani 
8. Narmada 9. Indira 10. Saraswathi 11. Agni 12. Cauvery 13. Naga 14. Kunani 15.Thiruthi 16. Palaar 17. Deva 18. Varuna 19. Sarayu. 20. Kanniga ( at the centre ).