As part of an ongoing effort by members of Healthy Lake Winona, I collected water samples from Boller’s Lake this week to help us understand and improve our local water quality. Even before reaching the shoreline, I began noticing dead fish floating at the surface. In a matter of five minutes, I counted over 50 dead fish, mostly small sunfish species. Unlike last summer’s fish kill in the Whitewater River, these fish didn’t die from toxic chemical runoff but more likely from a lack of dissolved oxygen in the water.
For those who are not familiar, low levels of dissolved oxygen in water bodies are typically a result of excess nutrient pollution. Nutrients, like nitrogen and phosphorus, are essential for plant growth and are found in fertilizers commonly applied to farm fields and lawns. Excess nutrients can run off from the land and enter water bodies, encouraging aquatic plant growth, especially algae.
While green algae produce oxygen through photosynthesis, high concentrations of algae near the surface reduce light penetration and kill aquatic vegetation underneath it. The increased decomposition of this dead plant material by bacteria and fungi consumes oxygen faster than it can be replenished, eventually lowering dissolved oxygen to levels that fish cannot survive.
Unfortunately, fish kills have become a common phenomenon in Minnesota lakes and streams, but I am hopeful that the frequency of incidents like the one in Boller’s Lake this week can be reduced with greater public awareness.
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For example, the rain gardens now being built in the city capture stormwater runoff from lawns and absorb nutrients before entering Lake Winona or the Mississippi River. The stenciled storm sewers in town are a friendly reminder to not dump chemicals or rake yard clippings into the storm sewers because they lead directly into our waterways.
Reducing or eliminating the application of fertilizers that contain phosphorus to your lawn can also make a significant difference by preventing nutrients from entering our water.
Visit the Healthy Lake Winona website, healthylakewinona.weebly.com, to learn more about how you can help prevent future fish kills in our lakes and streams.
Unfortunately, fish kills have become a common phenomenon in Minnesota lakes and streams, but I am hopeful that the frequency can be reduced with greater public awareness.