Just had to let that little tid-bit out, didn't ya. I have found a lot of walleyes in the big river's backwaters in the heat of summer.
A buddy and I were catching nice crappies in a chute one summer day when the actual temp was 98 degrees. The chute was only 8 feet deep but the crappies were tucked back in the weeds a ways so doing exactly what you describe got our hits. We were going to move and while pulling up the electric we saw a large school of walleyes casually swim right under us. We put the motor back down and tried casting to them but they didn't seem to be interested and in fact started to break the school apart by going into the weeds. That got re-interested in the spot and we did pop walleyes by fishing right up tight to those weeds. I always had assumed that in summer heat, especially with high skies, that waldos sunk to the bottom out on channel water. Not so and I've been back to prove it to myself.