Whitewater kayaking is the sport of paddling a kayak on a moving body of water, typically a river. Whitewater kayaking can range from a fun, carefree, splashy-splash float trip to a challenging, adrenaline-filled sport. Rivers are classified by difficulty into an International Scale of River Difficulty, ranging from Class/Grade I--a flat, slightly moving river--to Class/Grade VI, considered the limit of possibility. For most kayakers there is a significant difference in challenge between Class/Grade III (Moderate) and Class/Grade IV (Advanced).