Once upon time, there was a handsome man. His name was Batara Guru Sahala. He liked fishing. One day, he caught a fish. He was surprised to find out that the fish could talk. The fish begged him to set it free.
Batara Guru could not bear it. He made the fish free. As soon as it was free, the fish changed into a very beautiful woman. She attracted Batara Guru so much. He felt in love with that fish-woman. The woman wanted to marry with him and said that Batara Guru had to keep the secret which she had been a fish. Batara Guru aggreed and promised that he would never tell anybody about it.
They were married happily. They had two daughters. One day Batara Guru got very angry with his daughter. He could not control his mad. He shouted angrily and got the word of fish to his daugters. The daughters were crying. They found their mother and talked her about it.
The mother was very annoyed. Batara Guru broke his promise. The mother was shouting angrily. Then the earth began to shake. Volcanoes started to erupt. The earth formed a very big hole. People believed that the big hole became a lake. Then this lake is known as Toba lake.