Fish around lake, being at a loose end (4)
I believe the answer is:
idle
'being at a loose end' is the definition.
'fish around lake' is the wordplay.
'fish' becomes 'ide' (I've seen this before**).
'around' is an insertion indicator.
'lake' becomes 'l'.
'ide' going around 'l' is 'IDLE'.
(Other definitions for idle that I've seen before include "out of a job" , "Turn over" , "not working in > lounge" , "without basis" , "Workshy" .)