Being partial so South Eastern WI, I don't think you can find an area with a more diverse fresh water fishery. Lake Michigan Salmon and trout, travel a few hours south and I believe there is some very good Small mouth on the big lake.
In Racine, Wi on the Root river there is a phenomenal fall Salmon run and steel heads most of the winter. Some of these fish pulled out are running close to 40 pounds.
In the spring on Lake Winnebago you have the Walleye and White bass runs. Just insane fishing if you hit it right.
Northern IL, South WI you have the fox chain which has good fishing for more fresh water species.
Head to central WI and you have Petenwell flowage, Castle rock lake. The lakes together I believe are running 17k acres in size approximately.
Head to northern WI, and you have the largest concentration of freshwater lakes in the world.
And if this isn't enough you have the Mississippi, the grandad of rivers, to catch some great cold water cats.