Fire crews responded around 10 p.m. Sunday to the marina on a report of a boat on fire and arrived to find the vessel covered in flames that had also spread to a dock awning, Battalion Chief Craig Auzenne said.
Firefighters were able to extinguish the blaze but learned a man lived on the boat and his vehicle was still parked at the marina, Auzenne said.
The roof and walls on part of the boat collapsed in on itself, and the boat itself ended up sinking around 1 a.m. Monday, he said.
The Contra Costa County Sheriff's Office is now taking over the investigation and is working with a salvage team to bring the boat back up to the surface, Auzenne said.
The cause of the blaze remains under investigation, he said.