Legend of Aranmula Parthasarathi Krishna Temple
Legend has it that the idol which is worshipped at Aranmula had originally been installed at Nilakkal, a few miles to the south of Sabarimala. The Pandava brothers after crowning Parikshit as emperor of Bharat left on a pilgrimage visiting various holy places. In Kerala each brother installed his own ishta devata on the banks of the Pampa and nearby places and offered worship. Among them the one at Nilakkal was that of Lord Vishnu installed and worshipped by Arjuna.
Nilakkal in those days was a forest inhabited by some thousand souls. In course of time it became uninhabitable due to scarcity of water and frequent attacks by Marava marauders. The inhabitants were thus forced to make an exodus and they carried their idol with them. The merciful Lord Himself in the guise of a brahmachari wandered along the banks of the Pampa and showed them the place to live in. That was Aranmula. Since the people carried their idol in a raft made of six bamboo pieces the place acquired the name Aranmula ('aaru' being six and 'mula' meaning bamboo).
Origin of Boat Race in Aranmula Parthasarathi Temple
There was a Nambudiri Brahmin or Bhattatiri in a house called Mangattillam in Kattoor (literally a village of forests) some 6 km. east of Aranmula. He was an ardent devotee of Krishna and every month on Thiruvonam asterism he would feed a Brahmin after washing his feet as per custom. Once in the month of Chingom (August-September) he could not get a single Brahmin for the function. Bhattatiri was upset and did not know what to do. Suddenly a Brahmin appeared from nowhere and the much-pleased householder conducted the ceremony happily.
He requested the Brahmin to come again for the ceremony next Chingom. But the latter replied that he could be seen at Aranmula temple. He was none other than Hari who revealed Himself to the Brahmin in a dream
The next year, Bhattatiri left for Aranmula with 51 paras of rice and all the other materials for the feast and reached the temple in the early hours of Thiruvonam day. He also incurred all the expenses for pujas for the day in the temple. The thoni or boat carrying all these goods to Aranmula is called Thiruvonachilavu thoni. The tradition continues to this day.