See Ugandan dictator once in river (7)
I believe the answer is:
examine
'see' is the definition.
(I know that examine is a more specific form of see)
'ugandan dictator once in river' is the wordplay.
'ugandan dictator once' becomes 'Amin' (Idi Amin, 1928-2003).
'in' means one lot of letters goes inside another.
'river' becomes 'exe' (River Exe).
'amin' inserted into 'exe' is 'EXAMINE'.
(Other definitions for examine that I've seen before include "Thoroughly inspect" , "Inspect, study" , "Subject to scrutiny" , "Look closely at < test" , "Question (a witness)" .)