River classification is used to give a universal language to describe the difficulties on a river.
It is a somewhat subjective guideline, and is based on judging a river under certain conditions (i.e. normal water levels). Even minor changes in water levels can completely alter a classification.
- Class I (easy): Easy moving water with riffles and small waves. Risk is slight; most can do this on their own with little instruction. Self rescue is easy.
- Class II (novice / moderate): Straightforward rapids with wide, clear channels which are evident without scouting. Rocks or obstructions are easily missed with minimum maneuvering by trained paddlers. Swimmers are seldom injured and group assistance, while helpful, is seldom needed.
- Class III (intermediate / difficult): Rapids with moderate, irregular waves which may be difficult to avoid and which can swamp an open canoe. Complex maneuvering is required to avoid capsizing. Most danger can be avoided by experienced paddlers. Scouting is advised for inexperienced paddlers. Strong currents can make self-rescue difficult. Injuries while swimming are rare and self-rescue is usually easy but group assistance may be required to avoid long swims.
- Class IV (advanced): Powerful but predictable rapids. Requires precise handling in turbulent waters. May have large unavoidable waves or rapids. Constricted passage may demand very quick maneuvering. Rapids may flip a raft. Swims may be long and violent. Risk to injury is a great possibility. Assistance is usually required if capsized. Group assistance for rescue is often essential and requires practiced skills. A strong eskimo roll is highly recommended for kayakers. Considered the limit for open canoes.