Bad quality citrus by lake (8)
I believe the answer is:
ugliness
'citrus by lake' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.
'bad quality' is the wordplay.
'bad' becomes 'ugli' (I can't justify this - if you can you should believe this answer much more).
'quality' becomes 'ness' (I've seen this in other clues).
'ugli'+'ness'='UGLINESS'
Can you help me to learn more?
(Other definitions for ugliness that I've seen before include "Unsightly quality" , "Being nasty" , "Unattractiveness" , "Characteristic of a duckling" , "Hideous aspect" .)