Shallow lake fish goes round (4)
I believe the answer is:
idle
'shallow' is the definition.
(thesaurus)
'lake fish goes round' is the wordplay.
'lake' becomes 'L' (geographical abbreviation).
'fish' becomes 'ide' (type of fish).
'goes round' indicates putting letters inside.
'l' placed within 'ide' is 'IDLE'.
(Other definitions for idle that I've seen before include "Good-for-nothing" , "having been taken from service" , "Tick over like engine" , "Not in action or at work" , "Avoiding work, lazy" .)