GRADE 1: EASY
Fast moving water with very small waves and without obstructions. Passages are obvious and easily navigated. The risk to swimmers is slight; self-rescue is easy.
GRADE 2: NOVICE
Simple rapids with regular small waves, easy eddies, and gradual bends. Wide, clear channels make navigating easy without scouting. Little manoeuvering is required, and rocks and obstructions are easily avoidable. Rapids that are at the upper end of this difficulty range are designated Class II+.
GRADE 3: INTERMEDIATE
Rapids with strong currents, large waves, powerful hydraulics, and obstructions that may be difficult to avoid. Controlled maneuvers are often required to navigate, although passages are simple and have relatively little objective danger. Scouting is advisable for inexperienced parties. Rapids at the lower and upper end of this difficulty range are designated Grade 3- and Grade 3+ respectively.
Grade 4: ADVANCED
Difficult yet predictable rapids with large, irregular waves, boiling eddies, powerful hydraulics, steeper gradient, and some unavoidable obstructions. Passages are often difficult to recognize and require precise boat control and skillful manoeuvering to navigate. Scouting is likely necessary for safe passage, and self-rescue is difficult. Rapids at the lower and upper end of this difficulty range are designated Grade 4- and Grade 4+ respectively.
GRADE 5: EXPERT
Long, powerful, obstructed, and unpredictable rapids that expose paddlers to significant danger. Rapids are steep with large, unavoidable waves and major hydraulics, congested chutes, and many obstructions. Complex, demanding routes require precise boat control, “must make” moves and a high level of mental and physical fitness. What eddies exist may be small, turbulent, and difficult to reach. Scouting is necessary but may be difficult. Swims are dangerous, and rescue is often difficult even for experts. Proper equipment, extensive experience, and practiced rescue skills are essential.
GRADE 6: EXTREME
All previous difficulties increased to the absolute limit of practicability, suitable for teams of specially prepared experts only. Runs of this classification are rarely attempted and often exemplify the extremes of difficulty, unpredictability, and danger. The consequences of errors are very severe and rescue may be impossible.