Heron flying about European river (5)
I believe the answer is:
rhone
'european river' is the definition.
(river in France and Switzerland)
'heron flying' is the wordplay.
'flying' indicates anagramming the letters (letters fly around into new positions).
'heron' with letters rearranged gives 'RHONE'.
'about' acts as a link.
(Other definitions for rhone that I've seen before include "wherein runs rain in Arbroath" , "wine-producing area" , "European river and glacier" , "River at Avignon and Arles" , "French wine region" .)