It's pretty common for shallow lakes around here to have aerators installed. There is usually a motor installed in a small shed on shore that pumps air to the aerator somewhere in the middle of the lake. In mild years the DNR often doesn't run them but in hard winters they can prevent winter kills. They usually leave a spot of open water that never freezes. The lake I'm on has one. It's a small lake with maximum depth of 10'. Long winters with heavy snow cover (which blocks sunlight getting through the ice) can cause a lack of oxygen and significant fish kills. I haven't seen a hard winter kill in over 20 years but it's a very unpleasant site and the image of rotting fish 20' thick along the shoreline still pops into my head whenever I swim in the lake.
There are many other, even shallower lakes, in the immediate area and they do not have aerators installed. Mostly because they're too shallow to really sustain a sport fishery and the DNR doesn't care much if the carp and bullhead suffer losses. Despite the lack of aerator it still stakes a pretty bad winter to cause a fish kill.
Alan