| I |
Smooth water with a defined current, with riffles and small waves. Few obstructions, all obvious and easily missed with little training. Risk to swimmers is slight; self-rescue is easy. |
Easy |
| II |
Up to two feet waves. Straightforward rapids with wide, clear channels which are evident without scouting. Occasional maneuvering may be required, but rocks and medium-sized waves are easily missed by trained paddlers. Swimmers are seldom injured, and group assistance, while helpful, is seldom needed. |
Novice |
| III |
Up to five feet waves with defined navigation channels. Rapids with moderate, irregular waves which may be difficult to avoid and which can swamp an open canoe. Complex maneuvers in fast current and good boat control in tight passages or around ledges are often required. |
Intermediate |
| IV |
Requires previous inspection to define navigation channels and contingency plans. Intense, powerful but predictable rapids requiring precise boat handling in turbulent water. Scouting may be necessary the first time down. Risk of injury to swimmers is moderate to high. |
Advanced |
| V |
For professionals, extremely long, obstructed, or very violent rapids which expose a paddler to added risk. Swims are dangerous, and rescue is often difficult even for experts. |
Experts |
| VI |
For suicidals, these runs have almost never been attempted and often exemplify the extremes of difficulty, unpredictability, and danger. Rescue may be impossible. |
Extreme and Exploratory |
