Watertown Fire Rescue responded to a structure fire south of Watertown Saturday evening, at approximately 8:00pm.  Upon arrival, crews found the residence to be fully engulfed.  The house was unoccupied at the time of the fire.  There were also several other spot fires found on scene, all which appeared to be intentionally lit.  Watertown Fire Rescue crews assisted the Codington County Sheriff's Department on scene.  WFR was on scene for about 2.5 hours.  There were no injuries to report.