Knowlton, a 20-year-old resident of Olympia, Wash., was found after authorities responded to a call at 6:36 a.m. Tuesday reporting a body floating in the water.
Knowlton was wearing a white tank top shirt and blue jeans, according to police.
A blood trail led from outside a post office at Beach and Buchanan streets to a spot near where Knowlton's body was found, police said.
Someone had called police Monday night at about 10:30 p.m. to report fresh blood in the area of Laguna and North Point streets. Officers responded but didn't find a victim. The next day it was determined that the caller had mistakenly given dispatchers the wrong location, police said.
The death is being investigated as a homicide, but police are not yet releasing any information about possible suspects.
A dive team was headed out to the water where Knowlton was found to search for other evidence in the case this morning, police Officer Albie Esparza said.
Anyone with information about the death is asked to call the Police Department's anonymous tip line at (415) 575-4444 or send a tip by text message to TIP411.