Judge river minute (4)
I believe the answer is:
deem
'judge' is the definition.
(I've seen this in another clue)
'river minute' is the wordplay.
'river' becomes 'dee' (River Dee).
'minute' becomes 'm' (abbreviation).
'dee'+'m'='DEEM'
(Other definitions for deem that I've seen before include "Adjudge" , "Believe" , "View as" , "Regard in a specific way" , "Regard, consider" .)