A human body part was found on Sunday afternoon in the Rivière-des-Prairies in the Montréal-Nord borough.
Radio-Canada has since confirmed that it was a man's head.
After a 911 call at around 3 p.m., Montreal police spokesperson Julien Lévesque said that officers discovered an "inert part of a human body" on the banks of the river near Drapeau Avenue, close to the Pie-IX Bridge.
A security perimeter was set up on Sunday and a team of investigators was deployed, said Lévesque.
The circumstances surrounding the man's death are still unknown and his identity has not been released by Montreal police.