International River Grading System
I - Easy
Occasional small rapids, waves regular and low. The correct course easy to find, but care is needed with obstacles like pebble banks, protective works, fallen trees etc, especially on narrow rivers.
II - Medium
Fairly frequent rapids, usually with regular waves, easy eddies, or whirlpools. Course generally easy to recognise.
III - Difficult
Rapids numerous and with fairly high, irregular waves, broken water, eddies and whirlpools. Course not always easily recognisable.
IV - Very Difficult
Long and extended stretches of rapids with high irregular waves, difficult broken water, eddies and whirlpools. Course often difficult to recognise. INSPECTION from the BANK nearly always necessary.
V - Extremely Difficult
Long unbroken stretches of rapids with difficult and completely irregular broken water, submerged rocks, very difficult whirlpools and very fast eddies. INSPECTION from the BANK ABSOLUTELY ESSENTIAL.
VI - Absolute Limit Of Difficulty
All previously mentioned difficulties increased to the limit of practicability. Cannot be attempted without RISK OF DEATH.
Grading is merely another weapon in the canoeists armoury to allow a clearer evaluation of a set of circumstances, and should on no account be used as a substitute for prior inspection.