The Yellowstone, the longest free-flowing river remaining in the lower 48 states, is one of the few waterways along the Lewis and Clark trail that still looks and behaves much as it did when Captain Clark and his crew traveled down it in 1806. Unlike many other great western rivers whose currents have been stilled by dams and whose channels have been confined by levees, the Yellowstone remains free to move across much of its floodplain. As a result, it continually renews itself by carving new side channels, forming new islands, and creating bare sand beaches that lead to lush cottonwood forests. Periodic flooding also affects tributaries to the Yellowstone. These side channels provide important nursery areas for young trout and other fish, while the cottonwood forests offer prime habitat for hundreds of wildlife species, including beaver, river otter, whitetail deer, bald eagles, and many kinds of songbirds.