Class I
Moving water with a few riffles and small waves. Few or no obstructions.

Class II
Easy rapids with waves up to 3 feet and wide, clear channels that are obvious without scouting. Some maneuvering is required.

Class III
Rapids with high, irregular waves often capable of swamping an open canoe. Narrow passages that often require complex maneuvering. May require scouting from shore.

Class IV
Long difficult rapids with constricted passages that often require precise maneuvering in very turbulent waters. Scouting from shore is necessary, and conditions make rescue difficult. Generally not possible for open canoes. Boaters in covered canoes and kayaks should have the ability to Eskimo roll.

Class V
Extremely difficult, long, and very violent rapids with highly congested routes, which should always be scouted from shore. Rescue conditions are difficult, and there is significant hazard to life in the event of mishap. Ability to Eskimo roll is essential for boaters in kayaks and decked canoes.

Class VI

Difficulties of Class V carried to the extreme navigability. Nearly impossible and very dangerous. For teams of experts only, after close study has been made and all precautions have been taken.