A swimming expedition turned into tragedy near Marshalltown last night. The body of 19-year-old Allejandro Alviso-Vargas was pulled from the Green Castle Recreation Area Lake near Ferguson in central Iowa shortly after midnight.The Marshall County Medical Examiner pronounced him dead at the scene; an autopsy will be performed today. According to a report from the sheriff’s office, Alviso-Vargas was with a group of people when he decided to go swimming. After getting into the lake, he began having trouble and yelled for help. Friends drove into the water where he was last seen, but couldn’t find him. Sheriff’s deputies believe it was an accidental drowning and no foul play is suspected.