Look back over lake for fish (4)
I believe the answer is:
eels
'fish' is the definition.
(I've seen this before)
'look back over lake' is the wordplay.
'look' becomes 'see'.
'back' is a reversal indicator.
'over' means one lot of letters goes inside another.
'lake' becomes 'l'.
'see' in reverse letter order is 'ees'.
'ees' placed around 'l' is 'EELS'.
'for' acts as a link.
(Other definitions for eels that I've seen before include "Water snakes twisting in lees" , "Sea creatures found in lees" , "Elongated fish" , "Congers" , "Slender fishes" .)