White water rafting is a popular extreme sport. Rapids are classed in 6 Grades: Grade 1: Very small rough areas, might require slight maneuvering. (Skill level: very basic)
Grade 2: Some rough water, maybe some rocks, might require some maneuvering. (Skill level: basic paddling skill)
Grade 3: Whitewater, small waves, maybe a small drop, but no considerable danger. May require significant maneuvering. (Skill level: experienced paddling skills)
Grade 4: Whitewater, medium waves, maybe rocks, maybe a considerable drop, sharp maneuvers may be needed. (Skill level: whitewater experience)
Grade 5: Whitewater, large waves, large volume, possibility of large rocks and hazards, possibility of a large drop, requires precise maneuvering. (Skill level: advanced whitewater experience)
Grade 6: Class 6 rapids are considered to be so dangerous that they are effectively unnavigable on a reliably safe basis.
Rafters can expect to encounter substantial whitewater, huge waves, huge rocks and hazards, and/or substantial drops that will impart severe impacts beyond the structural capacities and impact ratings of almost all rafting equipment.
Traversing a Class 6 rapid has a dramatically increased likelihood of ending in serious injury or death compared to lesser classes. (Skill level: successful completion of a Class 6 rapid without serious injury or death is widely considered to be a matter of great luck or extreme skill and is considered by some as a suicidal venture)