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Longest North American Rivers
Rank	River	Country	Miles
1	Mackenzie	Canada	2,635
2	Missouri-Red Rock	US	2,540
3	Mississippi	US	2,348
4	Missouri	US	2,315
5	Yukon	US	1,979
6	St. Lawerence	Canada	1,945
7	Rio Grande	US	1,760
8	Nelson	Canada	1,600
9	Arkansas	US	1,459
10	Colorado	US	1,450

River Classifications

Class I - Easy
Waves small, passages clear; no serious obstacles.

Class II - Medium
Rapids of moderate difficulty with passages clear.

Class III - Difficult
Waves numerous, high, irregular; rocks; eddies; rapids with passages clear though narrow, requiring expertise in maneuvering.

Class IV - Very Difficult
Long rapids; waves powerful, irregular; dangerous rocks; boiling eddies; powerful and precise maneuvering required.

Class V - Extremely Difficult
Exceedingly difficult, long and violent rapids, following each other almost without interruption; riverbed extremely obstructed; big drops; violent currents; very steep gradient. Most rafting tour operators require testing and prior Class IV or better whitewater experience.

Class VI - Unrunnable
Just like it says - Don't even think about it!

Current Daily Streamflow Conditions

High

90th percentile

75th - 89th percentile

25th - 74th percentile

10th - 24th percentile

10th percentile

Low

Not ranked

The colored dots on this map depict streamflow conditions as a percentile, which is computed from the period of record for the current day of the year. Only stations with at least 30 years of record are used. The gray circles indicate other stations that were not ranked in percentiles either because they have fewer than 30 years of record or because they report parameters other than streamflow. Some stations, for example, measure stage only.