Internation Scale of Rapids Class I Moving water with a few riffles and small waves. Few or no obstructions. Class II Easy rapids with waves up to three feet, and wide, clear channels that are obvious without scouting. Some maneuvering is required. Class III Rapids with high, irregular waves often capable of swamping an open canoe. Narrow passages that often require complex maneuvering. May require scouting from shore. Class IV Long, difficult rapids with constricted passages that often require precise maneuvering in very trubulent water. Scouting from shore is often necessary, and conditions make rescue difficult. Generally not possible for open canoes. Boaters in covered canoes and kayaks should be able to roll.