St. Anthony Falls was the upper limit of commercial navigation on the Mississippi until two dams and a series of locks were built between 1948 and 1963 by the United States Army Corps of Engineers. The locks made commercial navigation possible above Minneapolis but, since the locks in Minneapolis are smaller than most of the locks on the rest of the river, the practical limit for many commercial tows was still further downriver. In 2015, the Upper St. Anthony Falls lock was permanently closed to stop the spread of invasive species, namely Asian carp. Following the closure, Minneapolis was once again the site of the head of navigation of the river.