A 50-year-old man was pronounced dead hours after he was found unconscious in the water near Discover Bay on Friday evening, a Contra Costa County sheriff's spokesman said.
The man was identified as Discovery Bay resident Jonathan Bloom, according to sheriff's spokesman Jimmy Lee.
Deputies from sheriff's office's marine services unit responded to a report of an unconscious and injured person in the water in the area of Indian Slough near the Discovery Bay main channel shortly before 5:30 p.m., Lee said.
The deputies found the man, later identified as Bloom, and took him to the marina to medical personnel, according to Lee.
Bloom was airlifted to John Muir Medical Center where he was pronounced dead several hours later, the spokesman said.
Deputies are looking into how Bloom ended up out of his boat and how he became injured, Lee said.
Anyone with information on the case is asked to call the marine services unit at (925) 427-8507.