Class I or Class 1

Easy: Moving water with small riffles and waves. Risk is slight; most can do this on their own with little instruction. Self rescue is easy. Good examples are the flat sections of broad rivers.

Class II or Class 2

Novice: Rapids are straightforward with wide, clear channels. Rocks or obstructions are easily missed with minimum manuevering by trained paddlers. Good examples in California are the lower American River (urban river in Sacramento) or parts of the lower Klamath River in Northern California.

Class III or Class 3

Intermediate: Rapids are moderate with irregular waves which are difficult to avoid. Complex manuevering is required to avoid capsizing. Most danger can be avoided by experienced paddlers. Large waves and/or strainers may appear. Strong currents can make self-rescue difficult. Scouting is advised for inexperienced paddlers.

This is where true whitewater begins. Great examples are the South Fork American River in central California and Middle Fork Salmon in Idaho.

Class IV or Class 4

Advance: Powerful but predictable rapids. Precise handling in turbulent waters. May have large unavoidable waves or rapids. Constricted passage may demand very quick manuevering. Rapids may flip a raft. Swims may be long and violent. Risk to injury is a great possibility. Assistance is usually required if capsized.

In California, the best examples are the North Fork American and Tuolumne River. Both run high in the spring with difficult rapids.

Class V or Class 5

Expert: Extreme conditions; long, difficult, violent rapids. Unavoidable waves and obstructions. Steep holes and/or drops. Demanding manuevers that come quickly before difficult passageways. Risks are high for injury and even death. Note: there are different degrees of Class V rapids. AWA.org has added another layer of classification strictly for the Class 5 rapids and rivers. 5.1, 5.2 etc with each level becoming as difficult as going from Class 4 to 5.

There are several class 5 examples; each with their own unique class 5 designations: Cal Salmon (Northern California), Cherry Creek (upper Tuolumne), Giant's Gap (upper North Fork American), and Forks of the Kern (Kern). All are serious Class 5+ runs in California.

Class VI or Class 6

Exploratory: The river or route is one of extreme difficulty. Mostly exploratory where danger is unpredictable. Consequence of errors may result in severe injury, life-threatening situations or even death. Many past Class 6 routes have been changed to Class 5 due to technological advancements in equipment. Also, the level of expertise has evolved over the past 10 years where some rapids which were deemed to be unrunnable, are now run with regularity by experts.