The Fall River originates in the remote southwestern corner of Yellowstone National Park in Wyoming, flowing south and west for approximately 64 miles before joining the Henrys Fork of the Snake River in eastern Idaho. This pristine spring-fed waterway drops nearly 3,800 feet in elevation along its course, carving through volcanic terrain and dense forests. Paddling opportunities on the Fall River range from scenic flatwater to challenging whitewater. The upper section, known as the Cave Falls Run, begins near Cave Falls Campground in Wyoming and offers stunning views of multiple waterfalls as it winds through Yellowstone's Cascade Corner. Below the park boundary, a popular 6-mile Class III section near Ashton, Idaho provides continuous action with 2-3 foot standing waves and technical boulder gardens. The lower Fall River from the Concrete CCC Bridge to Kirkham Bridge offers more moderate paddling suitable for packrafting.

Overall, the Fall River presents Class II to III+ rapids, requiring intermediate to advanced whitewater skills. The most challenging section near Ashton demands precise maneuvering through narrow passages and stronger currents. Paddlers should be comfortable with eddy turns and basic upstream techniques. The river's flow peaks in late spring and early summer with snowmelt, offering the best conditions for whitewater enthusiasts. However, its spring-fed nature provides relatively consistent flows year-round, extending paddling opportunities into late summer and fall.

The Fall River's ecosystem supports diverse wildlife, including grizzly and black bears, wolves, and a unique crossbreed trout known as the cutbow. Paddlers should maintain a safe distance from wildlife and practice proper food storage. Key landmarks include Cave Falls, a spectacular multi-tiered waterfall accessible by short trails, and the Initiation rapid - a challenging half-mile stretch in the Ashton section.

Primary access points are at Cave Falls Campground, near the Ashton Golf Course, and the Concrete CCC Bridge, with the nearby towns of Ashton and Island Park providing services. Safety considerations include cold water temperatures year-round and the presence of large wildlife. Paddlers should be aware of their surroundings and follow all park and forest service regulations. While primarily utilized for day trips, the Fall River's remote upper reaches offer potential for multi-day wilderness adventures for well-prepared paddlers.