William Navarro, 48, had forgotten his life jacket when he headed to Banks for a Friday evening rafting trip with his girlfriend, so he stopped at a nearby rafting company to borrow one.

But when the rapids of Mike’s Hole pitched him from the “cataraft” into the Payette River north of Boise, Navarro wasn’t able to haul himself back into the raft. He reportedly thought the buckles on the front of the Class 5 vest were foiling his efforts, Boise County Sheriff’s Sgt. David Anthony said Monday.

Navarro took the vest off and tossed it over the rear seat of the raft, Anthony said, but he was still unable to get back on board and ended up stranded in the fast-moving water without a flotation device. His girlfriend, Heidi Landa, tried desperately to help Navarro back into the raft, Anthony said.

As the raft approached another set of rapids, Navarro reportedly pushed himself away from the raft and floated downriver, Anthony said. Landa managed to steer the raft to shore with one oar — the other had been lost in the rapids — and ran along the bank until she lost sight of Navarro near Chief Parrish rapids, Anthony said. Landa then ran up the steep, brushy slope and flagged down a passing motorist who called 911 at 8:52 p.m. Friday.

Rescuers found Navarro face down in the water, unconscious and not breathing, just upstream of Beehive Bend, Anthony said. An air ambulance responded, he said, but efforts to revive Navarro were unsuccessful, he said.

“The lesson we take away from this is never, ever take your life jacket off until your float is complete,” said Anthony, who investigated the fatal accident.

If Navarro had kept the borrowed life jacket on, Anthony said, “his chances of survival would have been very, very good.”

“We don’t know why he didn’t try to swim to shore,” he said, noting that Navarro might have been exhausted by repeated efforts to get back onto the raft. The river water was flowing at an estimated 8 to 10 mph, Anthony said.

Friends and mourners flooded Navarro’s and Landa’s Facebook pages with grief and condolences Monday. Navarro was a longtime Boise resident.

Navarro’s death has been ruled an accidental drowning, Deputy Coroner Kuijas said. He estimating Navarro was in the water for a half hour or more before he was located. Rescue crews from Horseshoe Bend, Garden Valley and Cascade Raft Co. responded to the 911 call, Anthony said, and Navarro was spotted by a Horseshoe Bend firefighter on a jet ski.

Anthony said the Friday evening trip was reportedly Landa’s first-ever whitewater rafting trip, but Navarro was a more experienced rafter. He was positioned at the front of the two-seat catamaran-style raft, which features inflatable pontoons and a metal frame. Landa moved to the front seat after Navarro fell into the river, he said.

Anthony, who investigated the fatal rafting accident, said he returned to the scene Saturday and found the raft with the borrowed whitewater-rated life vest draped over the rear seat.