PHOTOS: The southbound lane of Highway 51 north of Wausau that was closed for several hours during the early morning and morning hours Wednesday has now reopened. Southbound 51 was down to one lane until just before noon. The fire was reported around 2 a.m. The lane closure was due to a semi-trailer fire. The trailer was hauling lumber. The Marathon County Sheriff’s Office said the fire started in the back of the trailer and the driver was able to escape safely.