Winter conditions may result in fish die-offs in shallow lakes
As ice recedes from lakes in Three Rivers Park District, Water Resources staff anticipate that several shallow lakes will have experienced fish die-offs over the winter.
The extensive snow depth on lakes this year shaded out all light transparency and reduced or limited the amount of oxygen aquatic plants produced under the ice. In addition, if the aquatic vegetation dies, the decomposition of the plants further depletes oxygen reserves in the water. The combination of these two factors can result in depleted oxygen levels in the water that create stressful conditions and eventually can cause fish to die.
Water Resources staff have been checking dissolved oxygen on several of the small lakes in the Park District. Staff have noticed that some of these lakes are experiencing fish die-offs and/or have had extremely low dissolved oxygen levels for significant portions of the winter. Three Rivers Park District installed aeration units on several lakes to provide oxygenated habitat for fish over the winter. However, the combination of low water levels from drought conditions going into the winter and extensive snow cover has resulted in extremely stressful conditions for the fish community.
Fish die-offs may be noticeable as ice recedes from lakes; they also may occur this spring as water temperatures begin to increase. When fish experience stressful conditions due to reduced oxygen over the winter, they may be more susceptible to infections as waters warm. Learn more about fish die-offs from the Minnesota Department of Natural Resources.