Rivers with Class I flat water interspersed with occasional Class II rapids: waves 1-2 feet high. Using a self-guided watercraft is an option.

*Best for young children and tentative adults.

Rivers with Class I - II water interspersed with Class III rapids: waves usually 2-3 feet high, passageways contain some obstacles. Rapids are challenging but not overwhelming.

* Best introduction to rafting for the widest range of people.

Rivers with Class I - III water interspersed with occasional Class IV rapids: waves and drops 4 feet high and sometimes higher, difficult passageways containing some obstacles. Unintentionally falling out of the raft may mean an uncomfortable "swim".

* Best for those with previous Class III experience wanting to try-out Class IV whitewater, and for athletic, adventurous first-timers.

Rivers with Class I - IV water and more difficult Class IV+ rapids: 4-5 foot waves and drops, complicated by difficult passages containing obstacles that require quick, precise maneuvering. Falling out of the raft and "swimming" in a rapid will be difficult.

* Best for those with previous Class III or Class IV experience wanting a more difficult whitewater challenge.

Rivers with Class I - IV+ water interspersed with long, tumultuous Class V rapids: 5-8 foot drops and obstacles that must be avoided. Falling out of the raft means an extremely difficult and potentially hazardous "swim".

* Best for those with previous Class IV & IV+ experience seeking the ultimate whitewater challenge.

Rivers containing rapids that are so difficult that safe passage is doubtful and chances of serious incident, injury and death are almost certain. If attempted and successful, luck deserves the largest portion of credit.