Whitewater kayaking is the sport of paddling a kayak on a moving body of water, typically a whitewater river. Whitewater kayaking can range from simple, carefree gently moving water, to demanding, dangerous whitewater. River rapids are graded like ski runs according to the difficulty, danger or severity of the rapid. Whitewater grades (or classes) range from I or 1 (the easiest) to VI or 6 (the most difficult/dangerous). Grade/Class I/1 can be described as slightly moving water with ripples but for that reason is not considered ‘Whitewater.’ Grade/Class II/2 can be described as moving water providing some small degree of challenge. Grade/Class VI can be described as extremely severe or almost unrunnable whitewater, considered almost certain death, such as Niagara Falls.