The International Scale of River Difficulty is a classification system used to rate the difficulty of navigating rivers and whitewater rapids. It ranges from Class I, which features easy, moving water, to Class VI, which includes extreme and potentially dangerous conditions. This scale helps paddlers and rafters assess the challenges they may face on a river. Each class is defined by specific characteristics, such as the size of waves, the presence of obstacles, and the skill level required. For example, Class III rapids have moderate, irregular waves and may require some maneuvering, while Class V rapids are very difficult and require advanced skills and experience to navigate safely.