Cove in film next to lake (5)
I believe the answer is:
inlet
'cove' is the definition.
(synonyms)
'in film next to lake' is the wordplay.
'film' becomes 'ET' (E.T. the Extra-Terrestrial).
'next to' is a charade indicator (letters next to each other).
'lake' becomes 'L' (geographical abbreviation).
'et' after 'l' is 'let'.
'in'+'let'='INLET'
(Other definitions for inlet that I've seen before include "Opening through which fluid can pass" , "Opening - passage" , "Small area of sea" , "Means of entry" , "Small bay or creek" .)