Class I (Beginner): Fast moving water with riffles and small waves. Few obstructions are present and easily missed with little training. Low- risk of injury to swimmers and self-rescue is easy.  

Class II (Beginner): Straightforward rapids with wide, clear channels which are evident without scouting. Occasional maneuvering may be required. May encounter rocks and medium-sized waves, which are easily missed by trained paddlers. Injury to swimmers is low risk and self-rescue is possible.

Class III (Intermediate): Rapids with moderate, irregular waves which may be difficult to avoid. Maneuvers are more complex in fast current and good boat control in tight passages or around obstacles are often required. Eddies are stronger with swift moving current making rescues more difficult. Scouting is recommended for inexperienced paddlers. Swimmers face a medium risk of injury and self-rescue becomes more unlikely and group rescue is often required.  

Class IV (Advanced): Intense, powerful but predictable rapids requiring precise boat control in turbulent water. Unavoidable obstacles such as waves, holes or large rocks may be present. These rapids often require must make moves around or through these obstacles to avoid swimming. Scouting is highly recommended for first time paddlers of these sections. Risk of injury to swimmers is moderate to high, and water conditions may make self-rescue difficult. Group assistance for rescue is often essential and requires practiced swift water rescue skills.

Class V (Expert): Extremely fast moving current and contain must make moves. Unavoidable features are present that require a highly experienced paddler to maneuver through or around them. Channels become narrower and currents and features become stronger and larger. Scouting is required but can be difficult. Swimmers will face a high risk of injury and swims may be long. Self-rescue is not an option and group assistance is needed. Well-trained swift water rescue skills are required. 

Class VI (Extreme): These rapids are not run commercially and require a professional level of paddler. These include features like waterfalls and may be in remote places where outside help is unavailable. Scouting is necessary but may be very difficult to access. Swimmers face an extremely high risk of injury or even death. Self-rescue is nearly impossible and will require group assistance with a high level of knowledge of swift water rescue skills.