Part of the Mississippi River is shut down today...Loose barges in Missouri forced the shutdownAuthorities say 15 barges fully loaded with coal were being pushed down the river when the tug boat cleared the bridge then somehow lost control.A four-mile stretch of the river is closed.Four barges sank. One was seen wedged against the bridge pier. Tugs corralled the other barges in the harbor.The U.S. Coast Guard is investigating the matter.