A weekend graduation party at the Waterloo Inn took a nasty turn.

Waterloo Regional Police say about 500 people were attending the party Saturday night for University of Waterloo engineering students when there was a dispute between a security person and another man.

Police say the man working security – a 23-year-old from Waterloo – was slashed across the face with a knife.

Police say he was treated in hospital and then released.

A 22-year-old Waterloo man was taken into custody.