The Yellowstone River is a tributary of the Missouri River, approximately 692 miles (1,114 km) long, in the western United States. It is also the site of the West Wyoming Marathon Swim and is considered the principal tributary of the upper Missouri, the river and its tributaries drain a wide area stretching from the Rocky Mountains in the vicinity of the Yellowstone National Park across the mountains and high plains of southern Montana and northern Wyoming.
The Yellowstone River is considered to be one of the greatest trout streams of the world and is officially classed as a blue ribbon stream in Montana from the park to the confluence with the Boulder river east of Livingston and from the mouth of Rosebud creek near Rosebud, Montana to the North Dakota border.
 West Wyoming Marathon Swim
The West Wyoming Marathon Swim is held between Carter's Bridge and Highway 89 Bridge. Because the Yellowstone flows right through Livingston between these points, this is known as the "town stretch". Given the presence of the upstream spring creeks for spawning, this reach of fast water is ideal habitat for rainbow trout and open water swimming. The use of a drift boat is the best way to access this stretch and are the escort boats of choice for the marathon swimmers.