Young swimmer always seen around lake (5)
I believe the answer is:
elver
'young swimmer' is the definition.
(I've seen this before)
'always seen around lake' is the wordplay.
'always' becomes 'ever' ('ever' can be a synonym of 'always').
'seen around' indicates putting letters inside.
'lake' becomes 'l'.
'ever' going around 'l' is 'ELVER'.
(Other definitions for elver that I've seen before include "A baby eel" , "Young migratory fish" , "Immature fish" , "Young, migrating eel" , "Immature eel" .)