There are two rivers in Switzerland which have three letters in their names. The river Aar and the river Inn
The River Nile has only four letters.
River Trent.
I think the longest name has 32 letters which is Bernadette Maria Rosena McLaughclin.
The Kalamazoo River.
No
The Rodil is a Spanish river with five letters.
axe
danube
Rio
Exe
ural