Take out permit to enter river (6)
I believe the answer is:
delete
'take out' is the definition.
(I know that delete is a type of take out)
'permit to enter river' is the wordplay.
'permit to' becomes 'let' (I've seen this in another clue).
'enter' indicates putting letters inside.
'river' becomes 'dee' (River Dee).
'let' inserted inside 'dee' is 'DELETE'.
(Other definitions for delete that I've seen before include "Cut, erase" , "Strike out or erase" , "Cancel, erase" , "Wipe out" , "'Erase, remove (6)'" .)