As per legacy says, sage Vilvamangalam Swami, who was an earnest devotee of Lord Vishnu. When the sage was doing pujas for Lord Vishnu in the holy spot of the temple, Lord Krishna used to visit him disguised as a little boy, with some mischievous pranks. The Swami used to enjoy the mischief of the boy and tolerate on most of the occasions. But one day when the naughty tricks of the boy became intolerable, the Swami got annoyed and pushed the boy aside with his left hand. The boy fell in the lake and immediately disappeared into a cave. The sage then heard a divine voice: “If you want to see me, come to Ananthankadu (the forest of Serpent Anantha)”. Then only Vilvamangalam Swami realized that the child was none other than God himself. With deep regret, he proceeded through the cave in search of the boy. Walking a long way towards the south, he finally reached a wooded area, which is the present Thiruvananthapuram. There he had a magnificent vision of Lord Vishnu in a reclining posture. It was at that holy spot the famous Padmanabha Swamy temple of Thiruvananthapuram was built. Devotees call it by the name Babia. As per the temple authorities, about 70 years back, a British soldier shot dead the crocodile in the lake. Surprisingly another crocodile appeared in the lake the next day and that soldier died by a snake bite within a few days. There is no river or pond nearby and the appearance of the crocodile remains a mystery. It is believed that there will be only one crocodile at any time, and when it dies another one appears mysteriously from somewhere.
Ananthapura Lake Temple is located in Kerala, India. Ananthapura Lake Temple was built in the middle of this lake. Still, you can see a huge cave in the north-east corner of the Ananthapura Lake which is believed to be the cave where the little Krishna disappeared. People believe that the cave-way connects Ananthapura temple to Thiruvananthapuram temple. In front of the cave is a small pit with water, which maintains a constant water level at all seasons, and is considered as sacred theertham. A divine crocodile guards the entrance of the cave and the temple. The temple is Priests feeding that crocodile.
The main deity of the Temple is Lord Vishnu seated on the serpent Anantha, while in the Sree Padmanabha Swamy temple at the capital city, the Lord is reclining on Anantha. In the sanctum sanctorum on either side of the main deity are the Goddess of Earth (Bhoodevi) and the Goddess of Prosperity (Sreedevi). In front of them stand Garuda and Hanuman with folded hands, praying devotionally. The unique feature is that the idols are not made of metal or stone, but constitute a rare combination of more than 108 medicinal materials called “Kadu Sarkara Yogam.