Investigators say carbon monoxide may be to blame for the deaths of 68-year-old Roger Dennis and 63-year-old Myles Correia.
"Carbon monoxide is one of the deadly killers which you just don't know, you can't really smell it," said Archie Steele, president of the California Bass Federation.
Steele is warning lake residents not to leave their safety up to chance.
He offers the advice after the two men were found dead in a Lake McClure houseboat.
"There is a lot of houseboats on the lake, and to me, they are no different than a home," Steele said. "You come, you stay and sleep on them. You really should have smoke detectors and CO detectors."
Deputies found the men after a friend reported they hadn't heard from Dennis in over a week.
What was supposed to be a welfare check at Dennis' houseboat, ended with a shocking discovery.
Steele says the deaths are unfortunate but reinforce the importance of working carbon monoxide detectors.
"There's times the CO detector might go off because the motor is running, but I would rather have that nuisance versus going to bed, saying good night and not waking up," Steele said.
At the moment, detectives have ruled out foul play.
An autopsy will be performed to determine the exact cause of death