Class 1 Easy and small rapids
Class 2 & 2+ some maneuvering small rapids and exciting.
Class 3 & 3+ Rapids with irregular waves and hazards that needs to avoid and more exciting
Class 4 Very difficult rapids lots of rocks, holes and hard to maneuvering
Class 5 Extremely difficult, long, and very violent rapids with several hazards, continue powerful rapids.
Class 6 Impossible to run the raft, Kayak may run this class of rapid, the more difficult rapid the more fun
(RIVER PO CHU AND MO CHU SELECTED FOR OUR RAFTING TRIPS IN BHUTAN ARE CLASSED BETWEEN 1 and 3+)