| Class 1 - Very easy - small and regular waves - passages clear - sandbanks - riffles |
| Class 2 - Easy - rapids of medium difficulty, with passages clear and wide - low ledges |
| Class 3 - Medium - waves numerous, high and irregular - rocks - eddies - rapids with passages that are clear, though narrow, requiring expertise in maneuvering - inspection usually needed |
| Class 4 - Difficult - long rapids - powerful and irregular waves - dangerous rocks - boiling eddies - passages difficult to scout but necessary - powerful and precise maneuvering required |
| Class 5 - Very difficult - long, very turbulent rapids, following each other almost without interruption - riverbed extremely obstructed - big drops, violent currents - steep gradient - scouting essential but difficult |
| Class 6 - Extraordinarily difficult - difficulties of Class 5 carried to extremes of navigability - nearly impossible and very dangerous - for teams of experts only, at favorable water levels and after close study with all precautions |