The boy, who was on a weekend camping trip with his family, was riding his motorbike along the river bank when he accidentally drove over the edge, according to the Lewis County Sheriff's Office.
The boy's father saw what happened and jumped in the river to save his son, but he was unable to reach him in the fast-moving water. The father was also swept away, but he was able to reach the shore about a half mile down river, deputies said.
Rescue crews found a piece of the boy's helmet snagged in a log jam about a mile down river from the campsite.
Deputies say the river is very cold and is running very fast due to to recent snow melt. That, along with the rough terrain, has made the search "extremely dangerous," according to the sheriff's office,.