You are absolutely right about the swampy areas you mention. That part of Missouri is often called "Swampeast Mo." It extends down into Arkansas. I lived around New Madrid,Sikeston and Bernie.
The Sam Hildebrand family you all are familiar with lived in those swamps. [Mingo Swamp]which is near Poplar Bluff or the lake you mentioned.
Mosquito's big enough to carry you off also live there, and there is a spraying program there.They come around with trucks with big tanks.
Those ditches are every mile in squares ,they run each way.