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Winter and Spring Fish Kills

As the weather warms, have you noticed dead fish along the shoreline? Unfortunately, winter fish kills are an annual occurrence, especially when we've had cold winters with abundant snowfall. During the winter, some fish become trapped in shallow pools of water and are unable to move to deeper water or downstream. Underwater vegetation creates oxygen in the water through photosynthesis, however, during the winter, plants are not able to photosynthesize as much due to ice and snow cover. As a result, the shallow water where fish get trapped has low dissolved oxygen, making it difficult for some fish to survive. 

Winter fish kills rarely result in the death of all fish in a lake and may even help naturally kill invasive common carp. Typically, wading birds and birds of prey will use the dead fish as a food source, and as the water levels rise in the spring, the fish will be carried downstream. Dead fish can also be buried or used as fertilizer. In general, fish kills will not have a significant negative impact on water quality. They can be reported to the Minnesota Duty officer at 651-649-5451. 

If you find a fish kill of the same size and species in the spring, the cause is most likely disease related. As fish spawn and compete for food in shallow spring waters, they weaken their bodies and become more stressed, making them more susceptible to disease and infection. If the fish kill includes fish of different sizes and species, you should notify the Minnesota Duty officer at 651-649-5451.