Yosemite National Park rangers announced on Monday that they have called off the search for a 19-year-old Sacramento hiker who was swept over the park’s Nevada Fall while swimming in the Merced River.

Officials called off the search for 19-year-old hiker Aleh Kalman because the river’s waters were too high, local television station KTVU reports. “He actually got swept away in the current, and unfortunately, got swept downstream and over the waterfall,” a Yosemite Park ranger told CNN.

According to the National Park Service, Kalman was attending a church event at Yosemite on Saturday when he decided to go swimming in the Merced River, which flows into the 600-foot Nevada Fall. Yosemite Park spokesperson Kari Cobb told KTVU that when witnesses last saw Kalman on Saturday afternoon, he was getting pulled toward the waterfall’s edge.

Kalman is not believed to have survived the fall. “Nevada Fall is a 600-foot waterfall, and we do believe that it is impossible to survive a fall like that,” a Yosemite Park ranger told CNN.

A California Highway Patrol helicopter aided the rescue efforts of a Yosemite Park search team, which spent the rest of Saturday looking for Kalman, KTVU reports. After calling off the search due to darkness, the team continued their efforts on Sunday morning, but failed to turn up any sign of the 19-year-old.

According to Cobb, the Merced River’s current was quite strong when Kalman disappeared, with temperatures in the low 50’s, KTVU reports. “It’s so much water, and it’s such a strong current. It’s just incredible that someone tries to go to swim there,” Balz Heeinger, a tourist from Switzerland, told CNN.