Authorities said a sport utility vehicle was northbound on Industrial Avenue when it left the road just north of Blue Oaks Boulevard and landed in the water at about 9 a.m.
The driver, seeking to save his own life, used a legally registered gun to shoot out a window as the SUV sank, a bystander said.
The 28-year-old man whose name wasn't immediately available is an armed security guard at Thunder Valley Casino, north of Sacramento. He sustained minor injuries in the crash.
The SUV eventually became submerged in the water.
The man said he was startled when his cell phone activated and that caused him to veer off the road and through the guardrail.
After blasting his way out of the car, the man used the old fashioned tool of flagging down a car to help get him to a hospital.