Whitewater paddling rivers are rated as Class 1 through Class 6 according to their difficulty and the severity of the "consequences" ensuing from a mistake. Be aware that the actual difficulty and danger presented by a river on any specific day can vary according to the water level, the presence of strainers or other temporary hazards, and the like. Always inspect a river before putting on, and don't let a river's rating trump your common sense.
Rivers (and paddling trips on them) are rated as follows:
Class 2 (Medium): Rapids are moderately spaced, waves up to 2 feet high. Crosscurrents are not strong. Abrupt drops and straightforward chutes over easy ledges up to 2 feet. The best route through rapids is easily discovered.
Class 3 (Moderately Difficult): Rapids are well defined though often blending together. Waves are irregular and choppy, up to 3 feet high. Strong crosscurrents. Narrow passages and obstacles require frequent maneuvering. The best route through rapids may only be visible by scouting from land. Regular eddies and strong hydraulics. Abrupt drops up to 3 feet.
Class 4 (Difficult): Rapids are long and involved, requiring precise boat control. Channels can be very narrow and twisted. Powerful irregular waves up to 4 feet high. Hydraulics can hold a boat and crosscurrents can overturn a boat. Drops up to 4 feet deep and holes up to 4 feet deep. Eddies may be squirrelly. Instant, often irreversible , decisions are necessary. The best route is not visible from the boat. Many rapids must be scouted the first time through.
Class 5 (Very Difficult): Very long, heavy, violent, turbulent water. Passages are very complex with difficulty followed immediately by difficulty. The best passage is not obvious even when scouted. Drops are over 4 feet and waves irregular and over 4 feet.Visibility is limited by obstructions, extreme gradient or waves. Eddies and resting spots are rare. The current is VERY powerful and whirlpools are possible. Water level is critical for running. The utmost in skill and performance is required of the paddler.
(The AMC doesn't paddle on Class 1 or Class 6 -- Class 1 is boring and Class 6 is insane -- so we haven't included those levels here.)
White water paddlers are rated as Class 1 (beginner), 2 (novice), 3 (intermediate), or 4 (advanced). They can paddle rivers that are equal to or below their ratings, and with the trip leader's approval, can paddle rivers one level above their own rating. If you are a new paddler, you would be interested in trips rated as Class 2.
Experienced paddlers may wish to refer to the Revised River Difficulty Scale...