(CNN) -- Near Yosemite National Park's beautiful Mist Trail, a young man lost his footing, slipping close to the edge of a waterfall. A female companion frantically grabbed for him, but stumbled.
Another hiker followed and the three were swept over the powerful 317-foot Vernal Fall, joining a deadly trend at the park this year.
Authorities at Yosemite National Park are still searching for two of the bodies from that deadly July accident.
And others are searching for answers to explain the recent rash of deaths at the national park in California.
This year, 16 people have died from incidents at Yosemite, rangers say. That is about twice as usual.
While five visitors have died this year from natural causes, the others were accidental and often entirely preventable.
Rangers say some visitors take part in dangerous practices such as hiking treacherous trails in flip-flops, or climbing over safety rails to get better pictures or swimming in waters that are perilously close to waterfalls.
Witnesses said the three hikers who were swept over the waterfall in July had climbed over a safety rail.
"We don't station a ranger in every possible dangerous place that's out there," said Kari Cobb, a park ranger. "People have to come here and realize that Yosemite is nature and it is a very wild place."
Bill Ott, a hiker, says he has seen people swimming in dangerous waters.
"We saw a number of people wading just steps from going into the faster water. It's crazy. Just crazy," he said.
Visitor Tim Timmerman says he has a plan to keep his family safe.
"We aren't worried because we think if you stay where you're supposed to stay, you're safe and it's exciting," Timmerman said. "It'll be a little scary for them but it's not dangerous if you do what you're supposed to do,"