Along the upper river, the gradient is steep and the water is fast, leveling and slowing as the river runs its course. The upper section has most of the whitewater rapids to be found along the river, and features dramatic topography including sink holes and caves, springs, and waterfalls, over tall sandstone and limestone bluffs, and many rock formations. At one point, a hike from the river up a narrow, boxed canyon leads to a waterfall, Hemmed-In-Hollow Falls, the highest of its kind between the Southern Appalachians and the Rockies. The river's current also gives life to well over 300 species of fish, insects, freshwater mussels, and aquatic plants.