Inexperienced Scuba Diver, 41, Drowns : Tragedy: Bobbi Jean Greenhead became separated from her group during night outing near county line.

A 41-year-old Granada Hills woman who completed her scuba training only last Saturday--and was described as a good athlete--drowned during a night dive off the coast just east of the Ventura County line, authorities said Thursday.

Bobbi Jean Greenhead, who owned a Studio City video and audio post-production company with her husband, was entering the water Wednesday night with a group of divers near Neptune’s Net restaurant north of Malibu when she became separated from her partner, Ventura County sheriff’s deputies said.

Patrisha Gyllenswan, 39, of West Los Angeles--with whom Greenhead had shared a certification dive last Saturday in Catalina--was holding Greenhead’s hand as they entered the water when Gyllenswan’s shoulder strap broke, according to Deputy Coroner Mitch Breese in Ventura.

Gyllenswan returned to the beach, assuming that Greenhead had swum past the breakers to meet the others, Sheriff’s Sgt. Keith Lazz said. She then “noticed a diving light that was separate from the others,” Lazz added. Gyllenswan alerted dive master Sigfus Sigurdsson of Manhattan Beach, who pulled the unconscious Greenhead from the water.

Sigurdsson immediately began cardiopulmonary resuscitation, authorities said, until paramedics took over and transported Greenhead to St. John’s Regional Medical Center in Oxnard, where Greenhead was pronounced dead at 11:33 p.m. Wednesday.

The original call to authorities occurred at 10:30 p.m.

Richard Greenhead, the victim’s husband, said his wife had taken training classes that involved “textbook stuff” and had dived in a swimming pool.

“She had made up her mind that she wanted to become a dive master,” her husband said. “She loved the water.”

After the autopsy on Thursday, Breese said, “There was no trauma and no injury. . . . Right now, we’re baffled. . . . In other words, we have no reason for her to drown.”

He said his office intends to investigate Greenhead’s medical history and inspect her rented scuba equipment for a malfunction.