Warmer Weather Brings Fish Kills to Light

Seasonal cycle of Minneapolis lakes fish kills is no cause for concern

Fish kills are again happening at Minneapolis lakes.

“Nearly every summer, as the temperature warms up and the water gets warmer, we get some fish that are dying from the rise in water temperatures,” said Deb Pilger, Director of Environmental Management for the Minneapolis Parks and Recreation Board.

According to the Minnesota DNR, oxygen depletion can be a factor contributing to fish kills in lakes across Minnesota as temperatures rise quickly and oxygen levels in water drops.  This change can stress fish, leaving them susceptible to disease.

Fish kills are often the result of Columnaris disease, a disease caused by the bacterium Chondrococcus columnaris. The bacterium is always present in fish populations but seems to affect fish in late spring / early summer when die-offs occur. Opportunistic infections tend to affect fish as water temperatures warm and fish are stressed from the energy they spent on spawning. Such infections can kill sunfish, crappies and bullheads, and occasionally, largemouth bass and northern pike.

“Typically, only those who own a home or cabin and have lakeshore access are aware of the fish kill odor,” said Pilger. “But because the paths and trails around Minneapolis lakes offers users such great access, more people notice it about this time every year.”

“We really try to keep an eye out for the spring and summer fish kills to make sure we get the fish cleaned up in a timely manner,” added Pilger.

Four Things to Remember About Summer Fish Kills:

1. Fish kills can happen yearly from common infections when water heats up quickly, or after spawning when fish are weakened and stressed.
2. Fish kills occur not just in Minneapolis lakes but in many lakes in Minnesota
3. Seasonal fish kills have no effect on the quality of the lake’s water for swimming or boating, the quality of the other fish in the lake or the ability to eat or consume fish from the lake.