International Scale of River Difficulty
EASY- Waves small; passages clear; no serious obstacles.
MEDIUM - Rapids of moderate difficulty with passages clear.
Most open canoeists should never tackle anything tougher than class II.
DIFFICULT - Rapids are longer and rougher than class II. Waves numerous, high, irregular; rocks; eddies; rapids with passages clear though narrow, requiring expertise in maneuver; scouting usually needed. Requires good operator and boating equipment.
VERY DIFFICULT - Rapids are generally longer, steeper and more heavily obstructed than class III rapids.Waves powerful, irregular; dangerous rock; boiling eddies; passages difficult to scout; scouting mandatory first time; powerful and precise maneuvering required. Demands expert boatman and excellent boat and outfit.
EXTREMELY DIFFICULT - Exceedingly difficult, long and violent rapids, following each other almost without interuption; riverbed extrememly obstructed; big drops; violent current; very steep gradient; close study essential, but often difficult. Requires best man, boat, and outfit suited to the situation. All possible precautions must be taken.
CLASS VI or U
UNRUNNABLE ! ! !
BLM California river recreation