The water flow of the Amazon is greater than the next ten largest rivers in the world combined. It it the second longest because the Nile just barely beats it in length.
When I was a kid there was an old guy in town that something happened to his mother and he ended up going to sea with his dad when he was nine years old. There was no Panama canal then. He said the sailing ships could take on fresh water 200 miles out off of the Amazon river. That is some current. He was a pretty neat old guy. Had some great stories.
Yes, the Amazon is a river’s river. If I recall my geography correctly, it is 60 miles wide at its mouth and affects weather and salinity 100 miles out to sea. Its drainage area is huge and gets a lot of rainfall because the area is tropical and the Andes “squeeze” most of the moisture out of the air when it is forced upward.