Large jug sheep found by river (4)
I believe the answer is:
ewer
'large jug' is the definition.
(I've seen this before)
'sheep found by river' is the wordplay.
'sheep' becomes 'ewe' (I've seen this before).
'found by' says to put letters next to each other.
'river' becomes 'r'.
'ewe'+'r'='EWER'
(Other definitions for ewer that I've seen before include "A wide-mouthed water jug" , "A wide-lipped jug" , "Large pitcher" , "Pitcher, water jug" , "Open vessel with handle and spout" .)