Leave floating on the river for show (6)
I believe the answer is:
reveal
'show' is the definition.
(revealing is a kind of showing)
'leave floating on the river' is the wordplay.
'floating' indicates an anagram (float can mean fluctuate or oscillate).
'on' indicates putting letters inside (as in clothing 'on' a person).
'the river' becomes 'r' (abbreviation for river).
'leave' with letters rearranged gives 'eveal'.
'eveal' going around '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" .)