An autopsy this week shows the cause of death for a man swept off the Wapama Falls bridge trail was fresh water drowning, a Tuolumne County sheriff’s sergeant said today.

The 66-year-old man lost his footing on the bridges at Wapama Falls and got flipped into the falls, witnesses told rangers last week. The death was reported at 1:45 p.m. Thursday to the Tuolumne County Sheriff’s Office.

“The autopsy was completed yesterday afternoon and the cause of death is listed as fresh water drowning,” Sgt. Andrea Benson with the Tuolumne County Sheriff’s Office told The Union Democrat today.

Because the death occurred within the boundaries of Yosemite National Park, National Park Service personnel are investigating. Federal authorities have not released the man’s name or hometown. A Park Service incident commander was handling notification of the man’s relatives.

Significant snowmelt runoff in the recent Central Sierra heatwave has helped swell waterfalls, creeks, streams and rivers in the Yosemite high country, including tributaries in the Upper Tuolumne River watershed like Wapama Falls.

Snow surveys in high elevation regions of Yosemite in April indicated this past winter brought the park its highest snowpack on record, Jamie Richards with Yosemite National Park public affairs said last week. In many locations above 8,000 feet elevation, snowpack measured more than 200 percent of average, based on water content.

Wapama Falls is the major cascade visible from O’Shaughnessy Dam that impounds Hetch Hetchy, which was 98 percent full when the fatal accident was reported last week.

It’s less than a three-mile walk to Wapama Falls from the parking area next to the dam. Wooden bridges traverse a lower section of the falls before the falls tumble into the reservoir. The falls and their proximity to the bridges are billed as incentives for hikers to make the walk.

“We do not know what caused him to slip and fall,” Richards said Monday. Asked if there was water on the bridge when he fell, Richards said, “We don't have an answer to that at this time.”

In late March this year, sections of wood beam railing on one of the bridges were broken or missing due to moving snow, avalanche, rockfall or intense runoff. Richards said bridge railings were fully repaired before the fatal accident on Thursday.

No other injuries have been reported at Wapama Falls this season, Richards said.

Two Los Angeles County men were swept to their deaths from the same bridge trail below Wapama Falls in late June 2011. Gregory W. Meyer, 53, of Whittier, and Richard Fox, 53, of Hacienda Heights, were swept off the bridge by high late-season runoff, authorities said. Fox’s body was recovered from Hetch Hetchy Reservoir.

According to the 2007 book “Off the Wall: Death in Yosemite,” in July 1978, a solo backpacker, 26-year-old Richard E. Dix, of San Mateo, went off-trail to sit above cascades at the base of the falls. Search-and-rescue personnel found his body sprawled in rocks below the base of the falls and above the reservoir.