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International Scale of River Difficulty
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Raft Trips

Colorado Whitewater Adventure
International Scale of River Difficulty

Please Note:
The rating of rivers is subjective. Rivers also change due to water levels, rocks that may shift on the riverbed, man-made influences, etc. On rivers rated on this website, ratings are based on medium water levels and should be used as a general guide. We have also used the minus or plus symbol to show that a river run may be a bit easier or harder than most runs of the same rating.


Fast moving water with riffles and small waves. Few obstructions, all obvious and easily missed with little training. Risk to swimmers is slight; self-rescue is easy. BOC note: Great for the whole family.


Straight forward 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. Swimmers are seldom injured and group assistance, while helpful, is seldom needed. BOC note: Great for the whole family.


Rapids with moderate, irregular waves which may be difficult to avoid and which can swamp an open canoe. Complex maneuvers in fast current and good boat control are often required; large waves or strainers may be present but are easily avoided. Strong eddies and powerful currents can be found, particularly on large-volume rivers. Scouting is advisable for inexperienced parties. Injuries while swimming are rare; self-rescue is usually easy but group assistance may be required to avoid long swims. BOC note: We recommend swimming ability for class III rivers and up.


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. A fast, reliable eddy turn may be needed to initiate maneuvers, scout rapids, or rest. Rapids may require "must" moves above dangerous hazards. Scouting is necessary the first time down. Risk of injury to swimmers is moderate to high, and water conditions may make self-rescue difficult. Group assistance for rescue is often essential but requires practiced skills. A strong Eskimo roll for kayakers is highly recommended. BOC note: Good swimming ability is recommended. With a professional raft guide, first time rafters with reasonable physical conditioning and a love of excitement should enjoy this river difficulty.


Extremely long , obstructed, or very violent rapids which expose a paddler to above average endangerment. 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. Scouting is mandatory but often difficult even for experts. A very reliable Eskimo roll, proper equipment, extensive experience, and practiced rescue skills are essential for survival. BOC note: Only for experienced boaters/rafters in great physical shape that want the ultimate challenge.


One grade more difficult than Class V. These runs often exemplify the extremes of difficulty, unpredictably, 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. This class does not represent drops thought to be unrunable, but may include rapids which are only occasionally run.

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