Class 1:Easy
Moving water with occasional small rapids. Few or no obstacles.

Class 2: Moderate
Small rapids with regular waves. Some maneuvering required but easy to navigate.

Class 3:Difficult

Rapids with irregular waves and hazards that need avoiding. More difficult manicuring required but routes are normally obvious. Scouting from the shore is occasionally necessary.

Class 4:Very difficult
Large rapids that require careful manicuring. Dangerous hazard. Scouting from the shore is often necessary and rescue is usually difficult. Kayakers should be able to roll. Turbulent water and large irregular waves may flip rafts. In the event of a mishap there is significant risk of loss, damage and/ or injury.

Class: 5 extremely difficult
Long and very violent rapids with servere hazards. Continuous, powerful, confused water makes route finding difficult and caution from the shore is essential. Rescue is very difficult or impossible and in the event of a mishap there is a significant hazard to life.

Class 6: Nearly impossible
Difficulties of class 5 carried to the extreme of navigability. Might possibly (but not probably) be run 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.