Fish by a lake -- perfect! (5)
I believe the answer is:
ideal
'perfect' is the definition.
('ideal' can be similar in meaning to 'perfect')
'fish by a lake' is the wordplay.
'fish' becomes 'ide' (I've seen this before**).
'by' says to put letters next to each other.
'lake' becomes 'l'.
'ide'+'a'+'l'='IDEAL'
(Other definitions for ideal that I've seen before include "Exemplar" , "Perfect; visionary" , "Conceptual" , "Ailed (anag)" , "Standard to aim for" .)