Wild heron river (5)
I believe the answer is:
rhone
'river' is the definition.
(I know that Rhone is a river)
'wild heron' is the wordplay.
'wild' indicates anagramming the letters.
'heron' anagrammed gives 'RHONE'.
(Other definitions for rhone that I've seen before include "River at Avignon and Arles" , "French wine region" , "Camargue river" , "River rising in Switzerland and flowing into the Mediterranean" , "River flowing through Lake Geneva" .)