A wind farm developer has called in the police after a 50m (164ft) test mast in Lincolnshire came down.
Enertrag UK, which wants to put up eight turbines at Baumber near Horncastle, said the mast had been vandalised.
The firm has offered a £5,000 reward for information leading to the conviction of anyone responsible.
The Baumber Windfarm Action Group condemned any vandalism but suggested the mast could have been blown over.
The mast was put up as a test ahead of the company's planning application.
It has been used to measure prevailing wind conditions and judge whether full-scale turbines are viable.
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