International Grading Scale of River Difficulty

Class I   Moving water with a few waves and small ripples.

Class II  Easy rapids with waves up to 1 meter 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.
          Rapids may require scouting from shore. Boaters in kayaks should 
          have the ability to Eskimo Roll.

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

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

Class VI  Water is at the extremes of navigability. Nearly impossible
          and very dangerous. For teams of experts only. Close study must be
          made ahead of time and all precautions taken.