The Soo locks were closed for several hours after officials found a suspicious package in the mail room.
Staff were evacuated from the buildings and the locks were closed from around 7:30 a.m. to 11 a.m.
Michigan State Police investigated the package and the scene and gave officials the "go ahead" to open the buildings again.
While the locks have been re-opened, the closure caused serious back ups for ships hoping to get through the locks. Ice blockage had boats backed up by about 7 boats yesterday, but the line up is now closer to 12 boats deep.