This winter’s heavy ice and snow cover may result in fish kills on inland lakes
MDNR warns of potential for fish kill after hard winter. Dead fish may not appear until weeks after ice-out.
Readers may be familiar with the phenomenon of summer kill, but according to the MDNR, winterkill is the most common type of fish kill and occurs during especially long, harsh winters - similar to the one experienced this year. The press release goes on to say that “shallow lakes with excess aquatic vegetation and mucky bottoms are particularly prone to this problem. Fish and other aquatic life typically die in late winter, but may not be noticed until a month after the ice leaves the lake because the dead fish and other aquatic life are temporarily preserved by the cold water.”
Once the lake is sealed off by ice, there is no more opportunity for oxygen from the air to mix with lake water. Dissolved oxygen concentrations begin to slowly decrease due to utilization by fish and other aquatic organisms. Plants produce oxygen through photosynthesis which is driven by light. So when sunlight penetrates the ice, aquatic plants can offset the process by producing oxygen under the ice. Alternatively, in the darkness under heavy ice and snow cover the plants begin to respire – removing oxygen from the water. An excess of aquatic plants put the lake at higher risk for dangerously low dissolved oxygen concentrations during periods of heavy snow cover.
It should be noted that for better or worse, ice cover is an important factor in inland lake ecology. A previous Michigan State University Extension article explored the role of ice in the annual cycle of temperate inland lakes.