The province's Special Investigations Unit has invoked its mandate following a Monday morning incident at Pinehurst Lake, south of Cambridge, involving Brant County OPP.
The OPP tweeted about the incident, in which an individual sustained a minor injury, but no further information was provided before the SIU investigation began.
The SIU investigates incidents in which a member of the public suffers an injury during interactions with police.
The Grand River Conservation Authority park remains open for visitors.
