The truck drive killed in the crash has been indentified as 31-year-old Conor Finnerty of Seattle.
The accident happened at about 11:00 a.m. Thursday morning on Almota Ferry Road at Casey Grade 32 miles east of Pomeroy.
Washington State Sergeant David DeVere said the driver was dead when emergency crews arrived.
"Witness statements reported that the truck was traveling too fast, it didn't make the curve and it left the roadway and entered the river," said DeVere.
Troopers said Finnerty was eastbound when he failed to negotiate a curve, overturned and went into the Snake River. Finnerty was wearing a seatbelt, and it's unknown whether drugs or alcohol were involved. Police are still investigating the accident to get a better idea of what may have caused the accident.