Neil Rhodes, the chief constable of Lincolnshire Police, has been suspended from duty.
The temporary chief has been relieved of his duties while "investigations are being considered" into potential conduct matters.
Police and Crime Commissioner Alan Hardwick has appointed Alec Wood as acting chief constable with immediate effect.
A statement from the commissioner’s office said: “It should be emphasised that suspension is a neutral act and it should not be inferred from the decision to suspend that the potential conduct matters have been proven.
“Following consultation with the Independent Police Complaints Commission (IPCC), the matters in question have been referred to them.”
Richard Davies, who came third in the Police and Crime Commissioner election in November, said: “I am shocked because Neil seemed very good in his role.
“I worked with home closely and it has come out of the blue. We will have to wait and see what happens.”
Reg Shore, who sits on the Lincolnshire Police and Crime Panel, said: “I was not told about this and it is a real surprise.”