Leave floating on the river for show (6)
I believe the answer is:
reveal
'show' is the definition.
(synonyms)
'leave floating on the river' is the wordplay.
'floating' is an anagram indicator (float can mean fluctuate or oscillate).
'on' indicates putting letters inside (as in clothing 'on' a person).
'the river' becomes 'r' (abbreviation).
'leave' with letters rearranged gives 'eveal'.
'eveal' enclosing 'r' is 'REVEAL'.
'for' acts as a link.
(Other definitions for reveal that I've seen before include "Divulge; make visible" , "Make known to others" , "Make known, expose" , "Disclose or uncover" , "Make known or visible" .)