Class I:
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:

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:

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:

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
may be 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 kayak roll highly recommended.
Rapids that are at the lower or upper end of this difficulty range
are designated “Class IV-” or “Class IV+” respectively. Limit
of open canoes.

Class V:

Extremely long, obstructed, or very violent rapids which expose a
paddler to added risk. 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 often difficult even
for experts. A very reliable kayak roll, proper equipment, extensive
experience, and practiced rescue skills are essential. Because of the
large range of difficulty that exists beyond Class IV, Class 5 is an
open-ended, multiple-level scale designated by class 5.0, 5.1, 5.2,
etc… each of these levels is an order of magnitude more difficult
than 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.

Grade VI:
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