Panning or prospecting for gold in the Truckee river ...
Along the Truckee you''d get bumped by kayakers and tubers ad people fishing, it can be a pretty active river area. There are places set up over in gold country in the Sierras with setups for that, near Placerville and Nevada it up in Alaska in a few places too. Make sure you check the rules/regulations before just starting to try it on your own, I think its pretty regulated these days ...