I was thinking about that danger (vs fun!) factor when I posted. I'm sure it's still very cold with the snow melt-off. & didn't that river used to be called (by Lewis & Clarke) the "quicksand river"? hahaha doesn't sound too safe does it? Still, the image of riding a horse into a river after a strenuous trek to cool off sure sounds enticing.
I've not been there on foot but I flew over quite a bit of the Sandy River
in a light-sport plane not long ago. I was surprised at how deep the canyon was.