Police said the discovery was made near to the plant in Haddington at about 6am on Monday. Detectives are currently treating his death as unexplained. The area has been cordoned off as forensic officers examine the scene.
A Police Scotland spokeswoman said: “Police in East Lothian are investigating following the discovery of a man’s body near to Haddington sewage works around 6am on Monday.
“The death is currently being treated as unexplained pending further inquiries.”