(CNN) -- Park rangers will resume their search Monday for a teenage swimmer who was swept over a nearly 600-foot waterfall in California's Yosemite National Park over the weekend.
Aleh Kalman had been swimming about 150 feet from the edge of the Nevada Fall on Saturday afternoon when he was caught up in the swift current of the Merced River, the National Park Service reported. The 19-year-old Sacramento resident had gone to the park with a church group, the park service said.
"We believe it's impossible to survive a fall like that," park spokeswoman Kari Cobb said.
Swimming above the 594-foot Nevada Fall is not illegal, but the river is marked by signs warning of the danger, Cobb said.
Searchers on foot and a California Highway Patrol helicopter crew attempted to find Kalman on Saturday but had to cut short efforts at nightfall. The grim task resumed Sunday, aided by three dog teams, the park service said.
The Merced River was running about 500 cubic feet per second on Saturday, "a very swift and powerful spring flow of water," the park service noted in a written statement. That had gone up to about 650 cubic feet per second on Sunday.
"Although the park received only 50 percent of normal snow pack, rivers within the park continue to run at high levels this time of the year," the service said. "Additionally, the water remains extremely cold and will be throughout the year."
Three other people were swept over another Merced River waterfall, the 317-foot Vernal Fall, in 2011.
Yosemite is about 200 miles east of San Francisco.