There was a fisherman who lived in Batak Land. His name was Batara Guru Sahala. When he was angling, he caught a fish. He was surprised to find that fish because the fish could tlk and it begged to set it free. He did accordingly.
After getting free, the free changed into a beatiful woman and Sahala fell in love with her. Sahala asked her to marry him and the women received him. However, she asked his promised not to tell anyone the secret that she was once a fish. They were very happily married, and got two daughters.
It was a pity on Sahala. One day when he got very angry with his daughters, he forgot his promised and he broke it. He told his daughters that they were the daughters of a fish.
His wife could not forgive him. Suddenly, the eart began to shake and volcanoes started to erupt. The eart cracked and formed a big hole. People said that tha hole became Lake Toba.