Young fish always found around lake (5)
I believe the answer is:
elver
'young fish' is the definition.
(I've seen this before)
'always found around lake' is the wordplay.
'always' becomes 'ever' (synonyms).
'found around' means one lot of letters goes inside another.
'lake' becomes 'L' (geographical abbreviation).
'ever' enclosing 'l' is 'ELVER'.
(Other definitions for elver that I've seen before include "Young migratory fish" , "slippery little thing" , "New slipper" , "Immature eel" , "Young, migrating eel" .)