There is a young man named Toba, One day he caught a fish but the fish had golden scales. It turned out that the fish was a beautiful girl and then Toba married her on the condition that his identity was kept secret.
Both of them later married and had a son named Samosir. One day Samosir made a mistake which made Toba angry and cursed him as a fish child. His wife then got angry and asked Samosir to take shelter somewhere. Furthermore, the water overflows which then becomes a lake called Lake Toba while the land where Toba's children take refuge is then called (the island) Samosir.