All rivers and creeks that are rafted or kayaked generally have a class. These classes are determined by water movement and obsticles through a specific section of river. The classes are number with roman numerals I-VI.
These are the requirements for each class:
Class I Rapids
Fast moving water with riffles and small waves. Few obstructions, all obvious and easily missed with little training.
Class II Rapids
Straightforward rapids with wide, clear channels which are evident without scouting. Occasional maneuvering may be required, but rocks and medium-sized waves are easily missed by trained paddlers. Rapids that are at the upper end of this difficulty range are designated “Class II+”.
Rapids with moderate, irregular waves which may be difficult to avoid. Complex maneuvers in fast current and good boat control in tight passages or around ledges are often required. Rapids that are at the lower or upper end of this difficulty range are designated “Class III-” or “Class III+” respectively.
Intense, powerful but predictable rapids requiring precise boat handling in turbulent water. Depending on the character of the river, it may feature large, unavoidable waves and holes or constricted passages demanding fast maneuvers under pressure. Rapids that are at the lower or upper end of this difficulty range are designated “Class IV-” or “Class IV+” respectively.
Extremely long, obstructed, or very violent rapids which expose a paddler to added risk. 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. What eddies exist may be small, turbulent, or difficult to reach. At the high end of the scale, several of these factors may be combined.
These runs have almost never been attempted and often exemplify the extremes of difficulty, unpredictability and danger. The consequences of errors are very severe and rescue may be impossible. For teams of experts only, at favorable water levels, after close personal inspection and taking all precautions. After a Class VI rapids has been run many times, its rating may be changed to an appropriate Class 5.x rating. – See more at: http://blueheronwhitewater.com/whitewater-rafting-north-carolina#sthash.n6Yh7x3U.dpuf