International River Classification
Class I: Easy. Fast moving water with riffles and small waves. Few obstructions, all obvious and easily missed with little training.
Class II: Novice. Straightforward rapids with wide, clear channels which are evident without scouting.
Class III: Intermediate. Rapids with moderate, irregular waves which may be difficult to avoid and which can swamp an open canoe.
Class IV: Advanced. Intense, powerful but predictable rapids requiring precise boat handling in turbulent water.
Class V: Expert. Extremely long, obstructed, or very violent rapids which expose a paddler to the above average endangerment. Drops may-contain, large, unavoidable waves and holes or steep congested chutes with complex, demanding routes. Rapids may continue for long distances between pools, demanding a high level of fitness.
Class VI: Extreme. One grade more difficult than Class V. These runs often exemplify the extremes of difficulty, unpredictability and danger. The consequences of errors are very severe and rescue may be impossible.