Class I:  (Easy)  Moving water with small disturbances on the surface and a few small waves. There is little to no danger to swimmers.

Class II: (Novice/Beginner)  Faster moving water with easily avoided rocks, holes, and waves. Danger to swimmers is still slight but care must be taken.

Class III:  (Intermediate)  Fast moving water containing various rocks, holes, currents, and waves that require skillful maneuvering to avoid. Swimmers could be at risk and may require help.

Class IV:  (Advanced)  Strong rapids, large waves, big holes, unpredictable currents, and dangerous obstructions requiring multiple maneuvers to get through or around. Swimmers are at risk and will require help to be rescued.

Class V:  (Expert)  All of the characteristics of Class IV with the added danger of being longer and containing more continuous features that may not be avoided. There is serious risk to swimmers and others may be of no help.

Class VI:  (Unrunnable)  Only a team of experts who carefully plan every aspect of this expedition would have hope of surviving these rivers and rapids.