The wild heron's river (5)
I believe the answer is:
rhone
'river' is the definition.
(Rhone River is an example)
'the wild heron's' is the wordplay.
'the wild' indicates an anagram.
'heron' with letters rearranged gives 'RHONE'.
(Other definitions for rhone that I've seen before include "12 wine region" , "Major French river, rising in Switzerland" , "Current" , "River rising in Switzerland and flowing into the Mediterranean" , "One following long course" .)