FAA spokeswoman Nancy Corey said two parachutes were seen, but it wasn't clear whether the pilots had ejected safely.
They crashed around 2:30 p.m. scattering debris on the river near Boardman, Corey said.
Rescue personnel were en route to the crash, she said.
"We're not sure what kind of planes they are," said Deputy Sarah Baker, with the Gilliam County (search) Sheriff's Office. "We're trying to get people out there to help and we're assessing the situation."