Sonoma County Sheriff's officials are investigating the death of a diver who was found Saturday morning on a kayak off Shell Beach in Sea Ranch, unresponsive and unconscious.

Rescue units from the Sea Ranch fire department and state parks department arrived at the scene shortly after a call about a kayaker in distress came in at about 10:40 a.m. A state parks diver swam out to the kayak to retrieve the diver.

"They brought him to the shore and he was already unresponsive," said Paul Eaton, an engineer with the Sea Ranch Fire Department.

Eaton said the diver was pronounced dead at the scene by a paramedic.

The Sonoma County Coroner and Sheriff's investigators are trying to determine the cause of death. There were early reports from emergency dispatchers that the man may have had a heart attack.

The diver's identity has not been released and no other information was available Saturday.