Solver reported on river vessel (4)
I believe the answer is:
ewer
'vessel' is the definition.
(I know that ewer is a vessel)
'solver reported on river' is the wordplay.
'solver' becomes 'you' (the person solving the clue!).
'reported' indicates a 'sounds like' (homophone) clue.
'on' says to put letters next to each other.
'river' becomes 'r' (abbreviation for river).
'you' sounds like 'ewe'.
'ewe'+'r'='EWER'
(Other definitions for ewer that I've seen before include "29 [VESSEL]" , "Jug with wide spout" , "from which liquid may be poured" , "Oversized jug" , "A wide-mouthed water-jug" .)