The body was spotted at about 12:05 p.m. near a footbridge in the creek between the Amtrak station and Marina Vista, Sylvia said.
The Contra Costa County Sheriff's Office dive team fished the body out of the water and it was taken to the county coroner's office, where an autopsy will be conducted Thursday.
Sylvia said the body was face down when it was found and police were unable to tell if it was male or female.
It was found between two beaver dams, which suggests that it most likely didn't wash up from the Bay.
Sylvia said that at this point police were investigating the case as a suspicious death.
"We treat everything as a homicide until we can prove otherwise," Sylvia said.