TFB- That is crazy interesting. I live on the Fox River in the Rochester Impoundment, after the Wateford Dam, but before the Rochester Dam.
Fishing a few years ago was absolutely awesome, then the RCDD drew the waterway down from 6 feet to 1 foot from October to April. Since then fishing has been absolutely horrible, to the point that I don't even fish it any more.
Been fishing the Fox for 20 years, and to date I have never caught a Yellow Bass after the Rochester Dam - only White Bass. I've speculated that many of the fish (including the Yellow Bass) went over the Rochester dam during the Winter Drawdown, as that was their only opportunity to stay alive given the low water level.
The fact that you're catching Yellow Bass for the first time on the Fox below Echo verifies what I thought had happened. You fish more than most and I know you know your fish species. The small Yellow Bass used to be thick in the Rochester Impoundment - you could catch 20+ any night of the week - now there is not a single one to be found.