Walleye are a native river species.. In most Lake/Res situations they resort to the most similar habitat to that of a river in-flow with sand/gravel/rock substrate, IF the proper river/in-flow situation is NOT present. The measure of flow, species present, etc., and variables we still don't understand are going to play a part.
We have a few Lakes here in KS that have a very small % of walleye reproduction in certain years where conditions are such that it works.
There are also a few lakes in central NE where this takes place to a very small degree.
In your example lake, if they are stocking 20,000 fish in that body size, I'm going to say those are fingerlings or possibly intermediates.. and doing so every year indicates to me there is little, if any natural recruitment.
