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.