| CLASS I | Moving water with a few ripples and small waves. Few or no obstructions.
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| CLASS II | Easy rapids with waves up to three feet and wide clear channels visible without scouting. Some maneuvering required. |
| CLASS III | Rapids with high irregular waves capable of swamping an open canoe. Narrow passages often requiring complex maneuvering and scouting from shore. |
| CLASS IV | Long, difficult rapids with constricted passages often requiring precise maneuvering in very turbulent water. Scouting from shore is often necessary, and conditions make rescue difficult. Not runnable in open canoes. |
| CLASS V | Extremely difficult, long and very violent rapids with highly congested routes nearly always require scouting from shore. Rescue conditions are difficult. Significant hazards to life in event of a mishap. Ability to Eskimo roll kayaks is essential. |
| CLASS VI | Nearly impossible to run and very dangerous. For teams of experts only after close study, having taken all precautions |
