Waste material not fresh dumped by a lake (5)

I believe the answer is:
offal
'waste material' is the definition.
(I've seen this before)
'not fresh dumped by a lake' is the wordplay.
'not fresh' becomes 'off' (as in food that's gone off).
'dumped by' becomes 'a' (I am not sure about this - if you are sure you should believe this answer much more).
'a lake' becomes 'L' (geographical abbreviation).
'off'+'a'+'l'='OFFAL'
Can you help me to learn more?
(Other definitions for offal that I've seen before include "Bits of waste meat" , "Carrion" , "Refuse - edible entrails of animal" , "Waste of carcase" , "Meat product" .)
