There are many lakes in southern MN which are classified as “Put and take” lakes. Natural reproduction is limited to nothing at all. Fish are stocked as fingerlings in any number of years. You can look this up on the “Lakefinder” option on the MN DNR website.
From the DNR:
Despite its limitations, stocking is a useful tool for some purposes:
Walleye are introduced to lakes that have been “rehabilitated” (that is, where the previous fish were deemed undesirable and removed). Where habitat is suitable, these introductions often establish self-sustaining fisheries.
In one of the most popular and effective uses of stocking, walleye fry are put in heavily used lakes that occasionally winter-kill. These lakes – many of them in southern Minnesota – are fertile, and walleye fry quickly grow into “keepers.” The fish may be given some protection with aerators to increase winter oxygen, but still, stocking these lakes is a gamble. The risk is losing great numbers of game fish before they can be caught. The payoff is desirable game fish where otherwise nongame fish would swim. Heavy use by anglers makes the gamble worth taking.
Walleye are also stocked in lakes with all the elements necessary for survival except suitable spawning areas. This approach works in lakes that once were natural walleye producers but that since have succumbed to farm runoff and lakeshore development. As fertilizers, septic-tank seepages and other sources of nutrients have enriched waters, algae proliferate and smother walleye eggs. In this instance, stocking is a prosthesis for an injured body of water.
In cases like these, people have a tendency to keep pretty much everything they can legally it seems. So you will most likely not see too many fish over 20″ in these lakes, and the fact that in “Normal” lakes that they would be good spawners would not necessarily apply to these lakes. 
