Green River narrowed close by? (6)
I believe the answer is:
endive
'green' is the definition.
(endive is a kind of green)
'narrowed close by?' is the wordplay.
'narrowed' becomes 'ive' (I can't explain this - if you can you should believe this answer much more).
'close' becomes 'end' (I've seen this before).
'by?' is a charade indicator (letters next to each other).
'ive' after 'end' is 'ENDIVE'.
'river' acts as a link.
I am not very happy about this link. It may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for endive that I've seen before include "Plant used in salads" , "Chicory-type salad vegetable" , "salad ingredient" , "Edible plant" , "Envied (anag.)" .)