That's a bummer. Bad river juju if someone pocketed it but I guess if it was a 20 blown here and another there it might not be so easy to figure out the scenario as if a wad were obviously by a vehicle.
I lost a small dry bag containing all my water clothes at Corn Creek in July, splash pants, hydroskin, shoes etc I easily get cold so I always pack clothes for all weathers. I can only think it fell off the trailer when we moved from campsite to ramp or was picked up from the ramp. I went back and scoured the place once I realized it was missing as I loaded the boat. For weeks I was hoping someone would turn it in to the Rangers. A river hex upon the person who made off with it, just a small river hex I don't want carnage just some level of discomfort or an expensive gear failure.