Police are searching the Oshawa Harbour after a fisherman discovered a female torso floating in the water.
The fisherman spotted the body part near the lighthouse in the harbour at around 8:30 p.m. Monday evening.
A preliminary examination conducted by the coroner's office identified "obvious" signs of trauma, according to Durham Regional Police.
Homicide investigators are now searching the lakefront and speaking to people in the area.
"We're going to be out there probably for most of the day with our public safety unit doing a grid search, doing a canvas of the area and the marine unit [will be] out there as well," said police spokesperson Dave Selby.
Police are also reviewing missing persons cases and calling for tips from the public in an effort to identify the deceased person.
"We'll be calling on the medical experts to help us determine DNA and that kind of thing," Selby added.
A post mortem examination will be conducted today to determine a cause of death.
Anyone with information about the incident is asked to contact Det. Short (ext. 5407) of the DRPS Homicide Unit at 1-888-579-1520.