The retreat of ice from Minnesota&8217;s shorelines may soon leave a grim reminder of winter&8217;s effects around some ponds and lakes. In most cases the dead fish are the result of a normal process known as &8220;winterkill.&8221; According to the Department of Natural Resources, when snow and ice cover a lake, they limit the sunlight reaching aquatic plants. The plants die from lack of sunlight, stop producing oxygen, and then decompose &8212; a process that also consumes oxygen. This oxygen deficit can kill other fish, although it seldom affects all fish.