(CNN) -- Three Yosemite National Park tourists climbed over a guardrail into the Merced River and were swept away Tuesday.
Witnesses who watched the group step into the swift, cold water about 25 feet from the cliff's edge urged them to come back to shore to no avail, park officials said.
Ramina Badal, 21, and Hormiz David, 22, both of Modesto, California; and Ninos Yacoub, 27, of Turlock, California, had hiked the popular Mist Trail to the top of Vernal Fall at about 1:30 p.m. Tuesday.
Vernal Fall is 317 feet high. The Mist Trail is the most popular trail in Yosemite National Park and attracts between 1,500 and 2,500 people a day, according to Kari Cobb, a spokeswoman for Yosemite National Park.
There are signs at the head of the trail that warn of danger and fast-moving water, the park's news release said.
"Visitors that want to go around guardrails ... it's up to them," Cobb said. "It's something that does happen and it's completely up to the visitor to know what safety concerns are around and take responsibility for their own actions."
Yosemite rangers continued to search Wednesday, concentrating on each side of the Merced River downstream from the fall, the release said.
After a huge winter snow and a cool spring and summer, the park's rivers and streams have been running at higher-than-normal levels for this year, and will remain high for several weeks, park officials said.
"So far we have seen no clues or no evidence of any of the bodies," said Cobb. "We are presuming that all three of them are dead ... we will scale up the search once the water levels have receded and we can insert crews to look for the bodies in the river safely."
Before Tuesday's incident, there had been three water-related deaths in Yosemite National Park this year.