A Larkspur man rescued early Wednesday morning from a capsized boat near San Quentin State Prison has died, and his female companion was in stable condition atMarin General Hospital, authorities said.

The two unidentified boaters — both Larkspur residents, in their 40s — were rescued shortly after 1 a.m. after their 14-foot motorboat capsized, said Marin sheriff’s Lt. Barry Heying.

They had set out from a dock on Corte Madera Creek at approximately 10 p.m. Tuesday and developed engine trouble in the bay, Heying said.

The man fell overboard while trying to restart the engine and capsized the boat while trying to climb back onboard, Heying said.

The boat eventually sank and the two victims spent more than an hour in the water, said San Rafael fire Battalion Chief Jeff Buscher.

The boaters were spotted by prison personnel from a lookout tower at approximately 1 a.m. and were rescued by San Quentin inmate firefighters, according to Buscher and media reports.

“”(Inmate firefighters) were the first responders on site and were able to pull the individuals out of the water,”” San Quentin Public Information Officer Lt. Sam Robinson told KTVU.

Sheriff’s deputies also responded in addition to firefighters from the San Rafael, Larkspur, Corte Madera, Marin County and Southern Marin departments, Buscher said.

Both victims suffered hypothermia and the man also suffered cardiac arrest, Buscher said. They were transported

to Marin General Hospital, he said.

Alcohol is believed to have been a factor in the incident, Heying said.