River pollution originally affected (4)
I believe the answer is:
camp
'affected' is the definition.
(camp can mean exaggerated or affected)
'river pollution originally' is the wordplay.
'river' becomes 'cam' (river in Cambridge, England).
'originally' indicates taking the first letters.
The initial letter of 'pollution' is 'p'.
'cam'+'p'='CAMP'
(Other definitions for camp that I've seen before include "Military settlement" , "Exaggerated in style for humorous effect - in tent?" , "Wildly theatrical" , "Coterie" , "Temporary settlement" .)