Class I: Very small rough areas, requires no maneuvering. (Skill Level: None)
Class II: Some rough water, maybe some rocks, small drops, might require maneuvering. (Skill Level: Basic Paddling Skill)
Class III: Whitewater, medium waves, maybe a 3–5 ft. drop, but not much considerable danger. May require significant maneuvering. (Skill Level: Experienced paddling skills)
Class IV: Whitewater, large waves, long rapids, rocks, maybe a considerable drop, and sharp maneuvers may be needed. (Skill Level: Advanced Whitewater Experience)
Class V: Whitewater, large waves, continuous rapids, large rocks and hazards, maybe a large drop, precise maneuvering. Often characterized by “must make” moves, i.e. failure to execute a specific maneuver may result in serious injury or death. Class V is sometimes expanded to Class V+ that describes the most extreme, runnable rapids (Skill Level: Expert)
Class VI: While there is some debate over the term “Class VI”, in practice it refers to rapids that are not passable and any attempt to do so would result in serious injury, near drowning or death. If a rapid is run that was once thought to be impassible, it is typically reclassified as Class V.