Dodge swimmer's head on river (4)
I believe the answer is:
scam
'dodge' is the definition.
(thesaurus)
'swimmer's head on river' is the wordplay.
'head' says to take the initial letters.
'on' is a charade indicator (letters next to each other).
'river' becomes 'cam' (I've seen this before**).
The first letter of 'swimmer' is 's'.
's'+'cam'='SCAM'
(Other definitions for scam that I've seen before include "fiddle" , "Swindle (sl.)" , "Fraudulent business scheme" , "'A con, deception (4)'" , "Fraudulent action" .)