Exploit of daughter on river (4)
I believe the answer is:
deed
'exploit' is the definition.
(I've seen this before)
'daughter on river' is the wordplay.
'daughter' becomes 'd'.
'on' says to put letters next to each other.
'river' becomes 'dee' (River Dee**).
'd' put after 'dee' is 'DEED'.
'of' acts as a link.
(Other definitions for deed that I've seen before include "What's done" , "Conscious act" , "Legal document for transfer of property" , "Action - legal document" , "Something done" .)