Dazzled by her beauty, that farmer asked her to marry him, and the beautiful lady accepted with one condition, he must not tell to anyone that the beautiful lady was a fish. after a year, the farmer and the beautiful lady had a son, their son had a bad habit. he always eat. he ate everything.
one day, their son ate all his parent's food. the farmer was angry, and accidentally, he said that he was a son of a fish. therefore, he had broke his promise to his wife, not to tell anyone that beautiful lady was a fish.
the beautiful lady and her son suddenly astonished. the ground where they stand, sparge water. the water keep flooding, and come into a big lake. that lake named Lake Toba