Person in charge lost, initially, in street in Paris by river (5)
I believe the answer is:
ruler
'person in charge' is the definition.
(I've seen this before)
'lost initially in street in paris by river' is the wordplay.
'initially' says to take the initial letters.
'in' indicates putting letters inside.
'street in paris' becomes 'rue'.
'by' is a charade indicator (letters next to each other).
'river' becomes 'r' (**).
The initial letter of 'lost' is 'l'.
'l' inserted inside 'rue' is 'rule'.
'rule'+'r'='RULER'
(Other definitions for ruler that I've seen before include "Despot perhaps" , "One who commands - often seen in the classroom" , "person holding sway?" , "Source of line" , "Aid to drawing straight lines" .)