The Secretary may acquire only such interest in the right-of-way designated “Crossing A” on map numbered 626-91007 as he determines to be necessary to assure public access to the banks of the Little Calumet River within fifty feet north and south of the centerline of said river. The Secretary may acquire only such interest in the rights-of-way designated “Crossing B” and “Crossing C” on the map dated October 1986 and numbered 626-80,033-B as he determines to be necessary to assure public access to the banks of the Little Calumet River and the banks of Salt Creek within fifty feet on either side of the centerline of said river and creek.