Officers responded at 2:39 p.m. to a report from a person who spotted the small body while walking along the waterfront west of the Tom Bates Regional Sports Complex, Berkeley police Lt. Kevin Schofield said.
The umbilical cord was still attached to the body of the baby boy, Schofield said.
Alameda County coroner's officials responded and took custody of the body.
"It's likely that it washed up to shore" from elsewhere, Schofield said.
He said Berkeley police and the coroner's bureau will investigate the case further to try to find out how the boy's body ended up there.