River difficulty is rated using the six-part International River Classification System. Individual rapids are rated by class, ranging from Class I to Class VI. Where two ratings are indicated for a specific rapid, the first rating applies to high water conditions and the second to medium-low water.

Class I - Easy

Suitable for novices in all boats.
Waves small and regular. Passages clear with occasional channel bars and artificial difficulties such as bridge piers.

Class II - Novice

Suitable for intermediate open canoe, novice closed canoe or whitewater boat with intermediate accompaniment.

Rapids of medium difficulty, with clear and wide passages. Low ledges, sweepers, snags, log jams and large protruding boulders may be present. Open canoes may ship water.

Class III - Intermediate

Suitable for advanced paddlers in open canoes and intermediate paddlers in whitewater and closed boats.

Waves numerous, high and irregular rocks, eddies and rapids with clear and narrow passages requiring precise maneuvering. Inspection usually needed. Upper limit for open canoes, although extended reaches at this level are not recommended.

Class IV - Advanced

Suitable for advanced paddlers in closed canoes and whitewater boats. Not suitable for open canoes.

Long rapids with powerful and irregular waves. Narrow passages through rocks and boiling eddies, requiring precise maneuvering. Course difficult to scout from the water. Inspection mandatory.

Class V - Expert

Suitable for expert whitewater paddlers only.

Extremely difficult, long and very violent rapids following each other almost without interruption. Channel bed is extremely obstructed. Big drops, steep gradient and violent current. Inspection essential but may be difficult due to nature of the terrain.

Class VI - Extreme and Exploratory

Suitable for teams of expert whitewater paddlers, at favorable water levels and with adequate provision for rescue.

Difficulties of Class VI carried to extremes of navigability. Nearly impossible and very dangerous.

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