A – Pools, lakes, or rivers with velocity under 2 MPH.
B – Rivers with velocity 2-4 MPH.
C – Rivers with velocity over 4 MPH. May have sharp bends or obstructions.
Whitewater Measure of Difficulty
CLASS I – Moving water a few riffles and small waves. Few or no obstructions.
CLASS II – Easy rapids with waves up to three 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 often necessary, and conditions make rescue difficult. Generally not possible for open canoes. Boaters in covered canoes and kayaks should be able to Eskimo roll.
CLASS V – Extremely difficult, long and very violent rapids with highly congested routes that nearly always must be scouted from shore. Rescue conditions are difficult and there is significant hazard to life in event of a mishap. Ability to Eskimo roll is essential for kayaks and canoes.
CLASS VI – Difficulties of Class V carried to the extreme of navigability. Nearly impossible and very dangerous. For teams of experts only, after close study and with all precautions taken.