A hiker took video Saturday of the men swimming in Palouse Falls in Franklin County before one of them disappeared under the water.
The park is still closed while officials search for the body of the 23-year-old Colville man.
Social media posts identified the man as Isaac Engell.
Herb Girton of Richland said he was hiking the state park's trails with some friends when he saw three men swimming in the raging waters below the falls.
Girton said he saw the men in the water at 5:13 p.m. and recorded them on his phone. Girton said the waves below the falls were about five feet tall.
By 5:21 p.m., two of the men resurfaced and escaped the water. The third never came back up.
"I didn't know he was in trouble," he said.
The Palouse River flows across the desert to make the dramatic 198-foot drop off basalt rock, thanks to geology carved by Ice Age floods.
A 25-year-old Spokane man died at the park last May while taking photos with his girlfriend.