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International Scale of River Difficulty

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The International Scale of River Difficulty is a convention used in most parts of the world to describe the relative difficulty and safety (or class) of a whitewater river or of a stretch of river.



There are six graduations, which are referred to as the class of the river or rapid. The notation convention is to use roman numerals. The six classes are:

The scale is somewhat arbitrary and subjective and there are often graduations, such as CIII+ being slightly more difficult than CIII and slightly less difficult than CIV-. The rating may also change depending on conditions, and sometimes even the type of boat (e.g. decked boats vs. open boats). In addition, the rating for an entire river may not always be consistent with the rating of portions of the river. For example, a river may be rated as CII overall, while portions of the river may be CI, CII or even CV because the more difficult sections are easily bypassed.

Class I

Easy passage through small waves or ripples. The route is clear with no obstacles.

List of CI rivers

Class II

Rapids of moderate difficulty with small waves and some obstacles. May require some manoeuvring.

List of CII rivers

Class III

More numerous, higher and irregular waves; some rocks and eddies; rapids with clear but narrow passages requiring expertise in manoeuvring; scouting usually needed.

List of CIII rivers

Class IV

Longer rapids with higher, more irregular and some dangerous rocks and boiling eddies. The route is difficult to scout and requires powerful and precise manoeuvring.

List of CIV rivers

Class V

Difficult, long and violent rapids with features and obstacles following each other almost without interruption. Extremely obstructed routes with big drops, strong current, very steep gradient. Difficult to scout.

List of CV rivers

Class VI

Formerly classified as unrunable by any craft. This classification has now been redefined as unraftable due to people having run mulitple Class VI around the world.

List of CVI rivers


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