The investigation is now at its early stages, and investigators have not released the identity of the man who drowned.
The coroner's office was on scene to piece together what happened, and California State Parks said a local rental company dialed 911 after they found out the man was drowning. Park rangers say the incident occurred near an area of the lake without lifeguards.
There were two men in the water and both were having trouble staying afloat. Action News learned that people in a nearby boat threw a flotation device to one man, but the second man did not make it.
Paramedics from American Ambulance attempted to save the man, giving him CPR for nearly 30 minutes. Park rangers say the area were they man drowned was about 10 to 15 feet deep, and they are advising swimmers to be cautious.
Mark DeLeon of California State Parks said, "This is open water. It's not like swimming in the swimming pool. You have wind, boats, and it's hot. Limit your alcohol consumption, and if you're not a solid swimmer, use a personal flotation device."
Investigators are now working to find out if alcohol was a factor or the man may have had a medical condition.
The man's identity is unknown, but authorities believe the man is in his 30's, and that he is Hispanic and from out-of-town.
