Lots of pretty good lakes in the area. Washington, Madison, Hanska, Elysian, Frances, Tetonka, German, Jeff. They are all pretty decent. Some are better than others for each species though, what kind of fish are you looking for mainly?
The MN is a good walleye bite too, but late fall and early spring are gonna be your best bets down there. Meaning starting at slug season till freeze up in fall or around the opener during spring. You can run it with a boat, but you gotta be careful. When landing in Mankato, it is tough to go very far also unless you have a small boat or jet.
The Blue Earth river is also a good walleye bite, but you are more walking that one or a real small boat or canoe. It usually turns on earlier in the fall than the MN does.