Waste away by a lake (5)
I believe the answer is:
offal
'waste' is the definition.
(thesaurus)
'away by a lake' is the wordplay.
'away' becomes 'off' ('off' can be a synonym of 'away'**).
'by' means one lot of letters go next to another.
'lake' becomes 'l'.
'off'+'a'+'l'='OFFAL'
(Other definitions for offal that I've seen before include "Liver, lungs etc" , "Waste material" , "Rejected parts of a carcase" , "Edible liver or heart of animal" , "Edible animal viscera" .)