Horse leads away behind river (10)
I believe the answer is:
clydesdale
'horse' is the definition.
(I know that Clydesdale is a type of draft horse)
'leads away behind river' is the wordplay.
'away' indicates an anagram (letters move away from their original places).
'behind' says to put letters next to each other.
'river' becomes 'clyde' (I've seen this before).
'leads' with letters rearranged gives 'sdale'.
'sdale' put after 'clyde' is 'CLYDESDALE'.
(Other definitions for clydesdale that I've seen before include "Heavy breed of draft horse from Scotland" , "Powerful breed of horse" , "Breed of carthorse" , "Draught-horse" .)