Once a Gandharva by name Thumburu lived in the vicinity of this lake. He was a devotee of the Lord Sri Venkateswara. He instructed his wife to take an early morning bathe in the lake and get ready for the Lord's worship in the central shrine. She was a little hesitant to take a dip in the cold morning.
The Gandharva could not control his temper. He cursed her to be frog in the lake. When she begged his pardon, she was told when the sage Agasthya visits the lake and tells his disciples of the vibrant power of the lake waters, upon hearing the words of the saint her frog from would vanish.
She was at once transformed into a frog. She lived there in the Kona Thirtham in a dark. One day as foretold sage Agasthya came there and was elaborating the potency of the lake waters. Hearing this account the frog into a Gandharva woman, redeemed of her curse.
Since the Gandhava Thumburu lived there for a while, the lake had his name for it.