I saw this sign after I descended from Hell’s Canyon Overlook and was driving towards the little town of Oxbow, Oregon. The potential flooding eluded to by the sign is from the nearby Brownlee Reservoir Dam on the Snake River.
When they say evacuate do they mean Monty Python “Run away, run away” evacuate or poop your pants evacuate?
After coming down from the Hell’s Canyon Overlook and traveling through part of the Canyon floor I traveled along the Snake River which separates Oregon and Idaho. Some of what you are seeing is a reservoir created by the Brownlee Dam, so while it may not look like a river, the water is, in fact, that of the Snake River.
The first few photos are from the Oregon side looking towards Idaho, the latter photos are from Idaho looking back at Oregon. The bottom photo is a small area which extended away from the reservoir and stopped near the top portion of the picture.