Police have identified the man found dead as 31-year-old Roger Hugh Shaw of Southeast Portland.
Police say Shaw was reported missing Jan. 3 and had a history of mental health issues and drug addiction.
There was no sign of trauma or foul play, according to police.
The medical examiner is awaiting toxicology results to determine cause of death.
PORTLAND, Ore. – Portland police said a body was found floating in Johnson Creek Saturday afternoon.
William Sanders spotted the body from a nearby apartment complex west of SE 92nd Avenue just before 1 p.m.
"No mistaking. It was quite obvious it was a body," he said.
Police said the body appears to be an adult, but they are not sure if it is a man or woman.
Officers blocked off the area while homicide detectives and forensic division members investigate.
"It could be a lot of different things," said Sgt. Pete Simpson. "Could be somebody who fell off of the bridge. Could be somebody that walked in the water, suicide, there's a number of different possibilities."
Divers removed the body from the creek at around 3:30 p.m.
An autopsy is scheduled for Sunday.
KATU's Emily Sinovic contributed to this story.