Fly-tippers have dumped 60 bags of asbestos-laden building materials on land near the Norfolk Showground.
The incident occurred at some point between Saturday, May 6, and Tuesday, May 9, on the boundary between the outdoor venue and the village of Easton.
It is believed the rubbish is from a commercial building renovation and contains asbestos, plasterboard and electrical items.
Mark Nicholas, managing director of the Royal Norfolk Agricultural Association (RNAA) which manages the Norfolk Showground, said: "This massive pile of rubbish is clearly from a commercial building renovation and includes not only asbestos and plasterboard but old fire alarm equipment.
"Some of the plasterboard is a distinctive shade of green and recognisable. This is no way to care for the environment.
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"Somebody must know who is responsible for this."
The RNAA is offering a reward for information about the incident that leads to a conviction.
People with information are asked to contact the RNAA by emailing info@rnaa.org.uk.
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