For example, the article on the Mississippi River gives its length as 2,320 miles.
The article on longest U.S. rivers lists it as 2,202 miles.
If you cite Wikipedia as accurate, which edit? One of the 1,000 previous versions of the article or maybe one of the as yet to be edited 1,000 more? Which one is the holy true version?
No matter what criteria you choose it doesn't have the greatest flow. Yes it is more than Iguazu but that still only makes it 7th