The temple is on the left bank of the Pampa River. The sacred jewels of Ayyappan (Thiruvabharanam) are taken in procession to Sabarimalai each year from Pandalam, and Aranmula Temple is one of the stops on the way. Also, the Thanka Anki (golden attire) for Ayyappa, donated by the king of Travancore, is stored here and taken to Shabarimala during the Mandala season (late December). Aranmula is also known for the watersports involving a spectacular procession of snake boats. It is also linked with legends from the Mahabharata.
It is one of the most important Krishna temples in Kerala, the others being at Guruvayur, Trichambaram, Tiruvarppu and Ambalappuzha.Also, it is one of the five ancient shrines in the Chengannur area of Kerala, connected with the Mahabharata. The Chengannur temple is related to Yuddhishtra; the Tiruppuliyur temple to Bheema; Aranmula to Arjuna; Tiruvamundur to Nakula and Tirukkadittaanam to Sahadeva). It has been glorified by the Tamil hymns of Nammalwar of the 1st millennium CE.
Legend has it that the Pandava princes, after crowning Parikshit left on a pilgrimage of India, and in Kerala, each of these brothers installed Vishnu on the banks of the Pampa and nearby places and offered worship. (Chengannur,Thrichittattu - Yuddhishtra, Tiruppuliyur - Bheema, Aranmula - Arjuna, Thiruvanvandur - Nakula and Tirukkodithanam - Sahadeva). It is said that Arjuna built this temple at Nilackal near Sabarimalai. and the image was brought here in a raft made of six pieces of bamboo to this site, and hence the name Aranmula (six pieces of bamboo).
Legend has it that Arjuna built this temple, to expiate for the sin of having killed Karna on the battlefield, against the dharma of killing an unarmed enemy. It is also believed that Vishnu (here) revealed the knowledge of creation to Bhrama, from whom the Madhukaitapa demons stole the Vedas.
There is yet another legend associated with Parthasarathy here. On the ninth day of the battle of Kurukshetra, the Kauravas reigned supreme under the leadership of Bheeshma, when Krishna motivated Arjuna to take initiative and vanquish his foe. Upon his hesitating to do so, Krishna jumped down in rage, and took up his discus; seeing this sight Bheeshma surrendered to him and Arjuna beseeched him not to kill Bheeshma, as it would bave been against Krishna's vow to take up arms in his battle. It is believed that it is this image of Krishna that is enshrined here, with a discus. Aranmula Mirror is also very much related to the history of this temple
The boat race: Snake boats from 48 Karas from Chennithala in the west to Ranni in the east participate in the watersport Vallomkali. These boats assemble at dawn and sail in pairs for about 2 hours. A snake boat is about 103 feet in length. Each boat has about 4 helmsmen 100 rowers and 25 singers. After the watersport there is an elaborate feast in the Aranmula temple.