French wetlands with no river to maintain (5)
I believe the answer is:
argue
'maintain' is the definition.
(thesaurus)
'french wetlands with no river' is the wordplay.
'french wetlands' becomes 'camargue'.
'with no' is a deletion indicator.
'river' becomes 'cam' (I've seen this before).
'camargue' with 'cam' removed is 'ARGUE'.
'to' is the link.
(Other definitions for argue that I've seen before include "Disagree violently" , "Present the case for" , "Debate, contend" , "Heatedly exchange views" , "Make a case" .)