Class I – Easy: Moving water with occasional small rapids. Few or no obstacles.
Class II – Moderate: Small Rapids with regular waves. Some maneuvering required but easy to navigate.
Class III – Difficult: Rapids with irregular waves and hazards that need avoiding. More difficult maneuvering required but routes are normally obvious. Scouting from shore is occasionally required.
Class IV – Very Difficult: Large rapids that require careful maneuvering. Dangerous hazards. Scouting from shore is often necessary and rescue is difficult. Kayakers should be able to roll. Turbulent water and large irregular waves may flip rafts. In the event of mishap, there is significant risk of loss damage and/or injury.
Class V- Extremely Difficult: Difficulties of class 5 carried out to the extreme of navigability. Might possible (but not probably) be run by a team of experts at the right water level, in the right conditions with all possible safety precautions, but still with considerable hazard to life.
Class VI – Extremely Dangerous: Classified as unraftable. All previous difficulties increased to the limit of practicability. Very confused, very violent, exploding and folding water so difficult that controlled navigation by raft is virtually impossible.