Jacksonville Sheriff's Office homicide detectives investigated a drowning in Julington Creek on Saturday night.
Police were dispatched to the Julington Creek Marina at 12807 San Jose Boulevard about 7:30 p.m.
Investigators said a man's body was found in the water.
It was unclear how the man died.
Police said they were speaking to witnesses and trying to notify next of kin.
The man's name was not immediately released.