The Snohomish County medical examiner said an autopsy revealed that his cause of death was drowning related to cardiac arrhythmia.
Witnesses on the Kingston ferry spotted Sweet's body floating in the water near the dock.
The ferry crew deployed a small rescue boat and brought the diver to the beach south of the dock. Firefighters on the beach performed CPR, but were unable to revive the diver, said Leslie Hynes, spokeswoman for Snohomish County Fire District 1.
Sweet was part of a group of divers who volunteer their time on a maintenance project at the underwater dive park. His friends say he was an experienced diver and knew the Edmonds Dive Park well.