Summer's Rising Heat Brings Fishs Kill to Light

Seasonal cycle of fish kills is no cause for concern

As strange as it sounds the increase in temperature and the appearance of dead fish and plants around Minneapolis lakes has a direct correlation.

“Every summer, as the temperature warms up and the water warms up, we get some fish that are dying from the rise in water temperatures," said Deb Pilger, Director of Environmental Management for the Minneapolis Park and Recreation Board. "They will just die off and that, along with the plant life in the lake that will decompose when it gets warm, will begin to smell.”

According to the Minnesota Department of Natural Resources, oxygen depletion can be a factor contributing to fish kills in lakes all across Minnesota. Heavy rains during early summer can cause unusual high runoff from fertilized lawns, athletic fields, golf courses and farm fields. The runoff carries nutrients into the lakes, which combined with hot weather, can accelerate the growth of algae.

“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.”

Species affected are usually sunfish, crappies and bullheads and occasionally, largemouth bass and northern pike. To ensure that this year's fish kill is due to normal causes, the Minnesota DNR is testing fish kill samples from Lake Harriet.

"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 and plant decomposition happen yearly through a combination of increased temperatures and increased rain
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.