This is the American version of a rating system used to compare river difficulty throughout the world. American Whitewater stresses that no rating system is exact. Paddlers should always consult a current guidebook or obtain first-hand descriptions of river status.
The Five Classes
Class I – Easy
Fast-moving water with riffles and small waves. Few obstructions, all obvious and easily missed with little training. Risk to swimmers is slight; self-rescue is easy.
Class II – Novice.
Straight forward, easy rapids. Occasional maneuvering may be required, but rocks and medium sized waves are easily missed by paddlers. Swimmers are seldom injured and group assistance, while helpful, is seldom needed.
Class III – Intermediate.
Rapids with moderate, irregular waves which may be difficult to avoid. Maneuvers in fast current and good boat control is often required; large waves, capable of capsizing a boat may be present but are easily avoided. Strong eddies and powerful current effects can be found, particularly on large-volume rivers. Injuries while swimming are rare; self-rescue is usually easy but group assistance may be required to avoid long swims.
Class IV – Advanced.
Intense, powerful but predictable rapids requiring precise boat handling in turbulent water. Depending on the character of the river, it may feature large, unavoidable waves and holes or constricted passages demanding fast maneuvers under pressure. Rapids may require “must make” moves above dangerous hazards. Scouting may be necessary the first time down. Risk of injury to swimmers is moderate to high, and water conditions may make self-rescue difficult. Group assistance for rescue is often essential and requires practiced skills.
Class V – Expert.
Extremely long, obstructed, or very violent rapids which expose a paddler to added risk. Drops may contain large, unavoidable waves and holes or steep, congested chutes with complex, demanding routes. Rapids may continue for long distances between pools, demanding a high level of fitness. What eddies exist may be small, turbulent, or difficult to reach.
At the high end of the scale, several of these factors may be combined. Scouting is recommended but may be difficult. Swims are dangerous, and rescue is often difficult even for experts. A very reliable eskimo roll, proper equipment, extensive experience, and practiced rescue skills are essential.