A hiker has been missing in Yosemite National Park since the holiday weekend after being swept away by a cold and fast-flowing creek as California’s epic winter snowpack melts.

Hayden T. Klemenok vanished while backpacking with a group at Upper Chilnualna Falls on Sunday, the National Park Service said in a statement.

“At approximately 2 p.m., he entered Chilnualna Creek near the trail junction, and his whereabouts are currently unknown,” the service said.

The section of creek is about a dozen miles south of Yosemite Valley and features a series of waterfalls and cascades that plunge hundreds of feet.

Klemenok’s parents told The San Francisco Chronicle that his friends said the day of the accident was hot and the 24-year-old from Petaluma had gotten down on all fours to wet his face, but his hands slipped and he went into the water.

“It’s the worst experience any parent or family should go through,” said Michelle Klemenok.

California authorities have been warning the public that rivers, streams and lakes are extremely dangerous this year because of the massive runoff. The water is so cold that a person can lose muscle control within minutes, officials say.

Despite the warnings there have been repeated tragedies. Nearly two dozen people have drowned or gone missing in California rivers since mid-April, according to Bay Area News Group, which has been tracking reports from local authorities.