Fisherman on the Yellowstone River, United States, 1997Photograph by Annie Griffiths BeltDeep in thought on his boat near the snowy banks of the Yellowstone River, a fisherman examines his bait. The Yellowstone River is the longest undammed river remaining in the lower 48 states, flowing for 670 miles (1,078 kilometers) through Wyoming and Montana before ending in North Dakota, where it joins the Missouri River.