Mouth of river makes us teary, upset (7)
I believe the answer is:
estuary
'mouth of river' is the definition.
(I've seen this before)
'us teary upset' is the wordplay.
'upset' is an anagram indicator.
'us'+'teary'='usteary'
'usteary' is an anagram of 'ESTUARY'.
'makes' is the link.
(Other definitions for estuary that I've seen before include "Wide river mouth" , "Broad river mouth" , "eg Thames, Humber" , "Wide part of a river where it meets the sea" , "Wide river-mouth" .)