Understanding the role of oxygen in our lakes and ponds

Warm weather, fertilizers, and excessive plant growth can decrease the oxygen levels in our lakes, rivers, and ponds.

The “pea soup” look of excessive algae growth in Lake Erie | Photo by Monica Day, MSUE
The “pea soup” look of excessive algae growth in Lake Erie | Photo by Monica Day, MSUE

Recent rains in Michigan have alleviated many drought driven issues on land, but it may not have helped our surface waters that much. Warm temperatures, reduced water levels, heavy phosophorous loading from surface runoff and end of season overgrowth of aquatic plants and algae can reduce oxygen levels in lakes, rivers and ponds. Oxygen that is in the water called “dissolved oxygen” abbreviated to “DO.”

Aquatic insects and animals need DO to breathe in the water. If DO in lakes, rivers and ponds drops too low, then aquatic populations will move away, fail to reproduce and decline or die. Plants do help create oxygen, but they also use it too, especially when they begin to decline at the end of the season. Animals, including insects and bacteria, continually deplete the DO in the water. This accelerates at the end of summer when water bodies are usually quite full of aquatic plants and algae and can result in a summer fish kill. Cooler weather can help turnover the water increasing oxygen levels and cold-water which allows DO to hold better. 

Low levels of DO, resulting in hypoxia, and no levels DO, called anoxia, are indicators of poor water quality. High levels of fertilizer, organic wastes and decaying matter coupled with extended seasonal warm weather are a cause for concern and increased need for monitoring.  When these conditions are present, we can expect to see an increase in algae growth and larger than normal algal blooms during the fall turnover events.

To learn more about water and water quality, contact Michigan State University Extension  Natural Resources educators who are working across Michigan to provide water quality educational programming and assistance. You can contact an educator through MSU Extension’s Find an Expert search tool using the keywords “Natural Resources Water Quality.”

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