The International Scale of River Difficulty is the American Whitewater version of the rating system used to compare river difficulty worldwide. The scale is not exact. Rivers do not always fit easily into one category, and regional or individual interpretations may cause misunderstandings. It is not a substitute for a guidebook, first-hand descriptions of a run, or other sources of river information. As river difficulty increases, the danger becomes more severe. As rapids become longer and more continuous, the challenge increases. Running an occasional Class IV rapid on a stretch of river is less consequential than dealing with an entire river run of this category.
Use river ratings cautiously!
- In extreme conditions: Allow an extra margin of safety between skills and river ratings when the water is cold, at higher flows, or if the river is remote and inaccessible.
- When visiting new regions: Boaters attempting difficult runs in an unfamiliar area should act cautiously until they learn how the scale is interpreted locally.
- As conditions change: A river’s difficulty may change at any point due to fluctuations in water level, downed trees, recent floods, geological disturbances, or bad weather.
- Stay alert for unexpected problems!
