White Water River Classes Class I. Easy. Waves small, passages clear; no serious obstacles. Class II. Medium. Rapids of moderate difficulty with passages clear. Class III. Difficult. Waves numerous, high, irregular; rocks; eddies; rapids with passages clear though narrow, requiring expertise in maneuvering. Class IV. Very Difficult. Long rapids; waves powerful, irregular; dangerous rocks; boiling eddies; powerful and precise maneuvering required. Class V. Extremely Difficult. Exceedingly difficult, long and violent rapids, following each other almost without interruption; riverbed extremely obstructed; big drops; violent currents; very steep gradient. Class VI. Unrunnable. Just like it says - Don't even think about it! P. Portage. Boats must be carried along the river bank to get around an unrunnable stretch of river.