To support my point, here is the AWA Rating scale. Look at how much of it is
subjective, without defining the subject. Terms like 'easy', 'difficult',
'easy to maneuver', 'easily missed', 'fast moving', 'complex'..... what boat
are they talking about? And what boater? Even reference to 'swimmers' leaves
quite a few assumptions to be made. As an open boater, I always am
challenged by the reference to 'waves that can swamp an open canoe'. And as
a rafter, I can hardly imagine doing an eskimo roll...

Read these descriptions, and imagine yourself in a huge raft. Then imagine
yourself as a novice in a squirt boat. The descriptions won't fit the same
river on the same day.

The Six Difficulty Classes
Class I: Easy. Fast moving water with riffles and small waves. Few
obstructions, all obvious and easily missed with little training. Risk to
swimmers is slight, self-rescue is easy.

Class II: Novice. Straightforward rapids with wide, clear channels which are
evident without scouting. Occasional maneuvering may be required, but rocks
and medium sized waves are easily missed by trained paddlers. Swimmers are
seldom injured and group assistance, while helpful, is seldom needed. Rapids
that are at the upper end of this difficulty range are designated "Class
II+".

Class III: Intermediate. Rapids with moderate, irregular waves which may be
difficult to avoid and which can swamp an open canoe. Complex maneuvers in
fast current and good boat control in tight passages or around ledges are
often required; large waves or strainers may be present but are easily
avoided. Strong eddies and powerful current effects can be found,
particularly on large-volume rivers. Scouting is advisable for inexperienced
parties. Injuries while swimming are rare; self-rescue is usually easy but
group assistance may be required to avoid long swims. Rapids that are at the
lower or upper end of this difficulty range are designated "Class III-" or
"Class III+" respectively.

Class IV: Advanced. Intense, powerful but predictable rapids requiring
precise boat handling in turbulent water. Depending on the character of the
river, it may feature large, unavoidable waves and holes or constricted
passages demanding fast maneuvers under pressure. A fast, reliable eddy turn
may be needed to initiate maneuvers, scout rapids, or rest. Rapids may
require "must" moves above dangerous hazards. Scouting is necessary the
first time down. Risk of injury to swimmers is moderate to high, and water
conditions may make self-rescue difficult. Group assistance for rescue is
often essential but requires practiced skills. A strong Eskimo roll is
highly recommended. Rapids that are at the lower or upper end of this
difficulty range are designated "Class IV-" or "Class IV+" respectively.

Class V: Expert. Extremely long, obstructed, or very violent rapids which
expose a paddler to above average endangerment. Drops may contain large,
unavoidable waves and holes or steep, congested chutes with complex,
demanding routes. Rapids may continue for long distances between pools,
demanding a high level of fitness. What eddies exist may be small,
turbulent, or difficult to reach. At the high end of the scale, several of
these factors may be combined. Scouting is recommended but may be difficult.
Swims are dangerous, and rescue is difficult even for experts. A very
reliable Eskimo roll, proper equipment, extensive experience, and practiced
rescue skills are essential. . . Because of the large range of difficulty
that exists beyond Class V, Class 5 is an open ended, multiple level scale
designated by Class 5.0, 5.1, 5.2 etc. . . Each of these levels in and order
of magnitude more difficult that the last. Example: increasing difficulty
from Class 5.0 to Class 5.1 is a similar order of magnitude as increasing
from Class IV to Class 5.0.

Class VI: Extreme and Exploratory. . . These runs have almost never been
attempted and often exemplify the extremes of difficulty, unpredictability
and danger. The consequences of errors are very severe and rescue may be
impossible. For teams of experts only, at favorable water levels, after
close personal inspection and taking all precautions. After a Class VI
rapids has been run many times, its rating may be changed to an appropriate
Class 5.x rating.