Class I - Easy. Smooth water; light riffles; clear passages, occasional sandbanks, and gentle curves. The most difficult problems might arise when paddling around bridges and other obvious obstructions.
Class II - Moderate. Medium-quick water; rapids with regular waves; clear and open passages between rocks and ledges. Maneuvering required. Best handled by intermediates who can maneuver canoes and read water.
Class III - Moderately difficult. Numerous high and irregular waves; rocks and eddies with passages clear but narrow and requiring experience to run. Visual inspection required if rapids are unknown.
Class IV - Difficult. Long and powerful rapids with standing waves; big hydraulic waves and boiling eddies. Powerful and precise maneuvering required. Visual inspection mandatory.
Class V - Extremely difficult. Long and violent rapids that follow each other almost without interruption. River filled with obstructions. Big drops and violent currents. Extremely steep gradient. Even reconnoitering may be difficult. Rescue preparations mandatory. Can be run only by top experts.
Class VI - Extraordinarily difficult. Paddlers face a constant threat of death because of extreme danger. Navigable only when water levels and conditions are favorable. This violent whitewater should be left to paddlers of Olympic ability. Every safety precaution must be taken.