River's inlet almost diverted (4)
I believe the answer is:
nile
'river's' is the definition.
(Nile River is an example)
'inlet almost diverted' is the wordplay.
'almost' means to remove the last letter (most of the word but not all of it).
'diverted' indicates anagramming the letters (each letter get diverted elsewhere).
'inlet' with its final letter removed is 'inle'.
'inle' is an anagram of 'NILE'.
(Other definitions for nile that I've seen before include "River that's Blue and White" , "River of eastern Africa" , "Egypt's river" , "World's longest river" , "Cleopatra's river" .)