smokey420:
If I remember correctly, Lake Arbutus east of Black River Falls may have channel catfish. I know we have caught them in the outflow from the lake.
Finding flatheads in a lake may be possible, but as I can’t recollect any off the top of my head. It would seem that the best water to fish flats would be the MIssissippi R.
Another comes to mind is Lake Koshkonong southwest of Fort Atkinson. This lake is an impoundment of the Rock River and may have flats. I am sure it has channels.
Mark