Black lagoon spoiled city (7)
I believe the answer is:
bologna
'city' is the definition.
(Bologna is an example)
'black lagoon spoiled' is the wordplay.
'black' becomes 'b' (as in pencil classifications).
'spoiled' indicates an anagram.
'lagoon' anagrammed gives 'ologna'.
'b'+'ologna'='BOLOGNA'
(Other definitions for bologna that I've seen before include "Italian province" , "Capital of Emilia-Romagna" , "North Italian university city" , "Italian city - smoked sausage" .)