Anyone who finds several or more dead fish in a lake or stream can help by reporting these fish die-offs, which happen occasionally and usually result from natural causes.
“It can be unsettling and concerning to find a number of dead fish,” said Tom Burri, limnology consultant with the Minnesota Department of Natural Resources who deals with water quality issues related to fisheries. “We hope people will help us out by reporting dead fish right away so we can determine if an investigation is needed.”
People should call the state duty officer at 651‐649‐5451 or 800‐422‐0798 to report fish die-offs. Doing so provides a single point of contact for the incident. The point of contact is available 24 hours per day, seven days per week. An early report also allows timely water samples or other response actions to be taken if needed.
If there is an immediate threat to life or property, call 911 first. For general information requests, people can also contact area DNR fisheries offices, but this is not the best way to report fish kills.
Bacteria a common culprit
One University of Minnesota study estimated that 500 fish die-offs happen each year in Minnesota.
In spring and summer, groupings of dead fish are usually the result of a common bacterial infection referred to as columnaris. Columnaris tends to affect fish as water temperatures warm and fish are stressed from the energy they spent on spawning. Columnaris infections can kill sunfish, crappies and bullheads, and occasionally, largemouth bass and northern pike.
Most fish diseases and infection issues found in nature tend to be concentrated in fish of a specific species and size range. In contrast, when an individual observes dead fish of vastly different sizes and from multiple species, human activity is a more likely a cause.
“People should try to describe the fish types and sizes they see when making a report. That kind of information helps immensely,” Burri said.
Human causes of fish kills can include water discharged at high temperatures, toxic chemicals discharged or spilled, pesticides and fertilizers, manure runoff, and low oxygen levels in a lake resulting from storm water that runs off urban or rural landscapes. Often, there are multiple causes contributing to fish deaths.