Stronger fish survive low oxygen levels. When lakes freeze over the oxygen level drops. After thawing there is usually some weaker fish that didn't make it. More so in colder regions with longer periods of ice cover. But in the swamp I wondered why the minnows died so fast. So I drop 1 in the water. It didn't swim too far before gasping at the surface then dying. This was late summer and could have been several reasons for it including combonations of things. But when there is several minnows in a bucket of water, the minnows gasp at the surface when the oxygen level drops. If there is nothing to oxygenate the water the minnows die. The fish in a larger body of water like the swamp will find the areas with better oxygen levels or die. Thats why some areas produce well certain times of the year and produce nothing other times at the Geneva Swamp.  

WE USED KAYAKS TO GET IN THERE - A FEW YRS BACK, ONCE YOU GOT OUT THERE IS WAS EASY TO GET AROUND, FINDING A SPOT TO LAUNCH WAS THE ONLY PROBLEM, IT IS WORTH GOING IN THERE, IF YOU HEAD ALL THE WAY THROUGH THAT LITTLE PATHWAY YOU SEE FROM 79, YOU WILL END UP AT A SPILL WAY - THERE WERE 2 GUYS FISHING THERE AND WONDERED WHERE WE CAME FROM.

There are pike there.  Some big ones, but the only ones I have caught there have been EXCEPTIONALLY skinny.  Some channels and LOTS of bowfin.