The Yellowstone River originates in Wyoming and flows through Yellowstone National Park before entering Montana at Gardiner. From the park boundary to Livingston, the river flows north through Paradise Valley, flanked by the Absarokee Mountains on the east and the Gallatin Range on the west. It continues in a northeasterly direction from Livingston and meets up with the Missouri River just across the North Dakota border.
The Yellowstone has survived as one of the last, large, free flowing rivers in the continental United States. It is still the longest undammed river in the lower 48 states. From the clear, coldwater cutthroat trout fishery in Yellowstone National Park to the warmer water habitat at its mouth, the river supports a variety of aquatic environments that remain relatively undisturbed. The adjacent terrestrial environment, through most of the 550 Montana miles of river, is an impressive cottonwood-willow bottomland.
The river has also been a major factor in the settlement of southeastern Montana, and retains much cultural and historical significance. The Yellowstone River is considered one of the great trout fishing locations in the world.