| Class | Difficulty | Description |
|---|---|---|
| 1 | Easy | Waves small; passages clear; no serious obstacles. |
| 2 | Medium | Rapids of moderate difficulty with passages clear. |
| 3 | Difficult | Waves numerous, high, irregular; rocks; eddies; rapids with passages clear through narrow chutes requiring expertise in maneuvering. |
| 4 | Very Difficult | Long rapids; waves powerful, irregular; numerous rocks; boiling eddies; powerful and precise maneuvering required. |
| 5 | Extremely Difficult | Exceedingly difficult; long and violent rapids, following each other almost without interruption; riverbed extremely obstructed; big drops, violent current and very steep gradient. |
| 6 | Unrunnable | Don’t even think about it! |