Shortly after Memorial Day, watershed residents often begin to observe fish die-offs in local lakes. This was a common sighting in the lakes around Scott County during late spring/early summer in previous years. In 2014, testing confirmed that columnaris bacteria was the cause of the die-offs in Carls (McMahon) and Cedar Lakes, and it is suspected that this bacteria was also the likely cause of the die-offs seen in lakes around the area.
As we approach the same season this year, it is important to keep in mind that the die-offs caused by Columnaris disease are a natural occurrence and only affect a small percentage of the fish populations in our lakes. There is no known cure, but is believed to have little effect on the long-term health of fish populations.
Columnaris disease is caused by a bacteria that is constantly present in fish populations, but does not typically cause death except during spring spawning season when fish are stressed. Most commonly observed die-offs are of crappie and sunfish populations. Symptoms of Columnaris disease are discolored patches, sloughing of scales and eroded gill filaments. The DNR recommends that diseased fish not be consumed, but healthy fish from the same lake can be safely eaten. The columnaris bacteria are not know to pose a health threat to humans.
If you observe large fish die-offs on any of the lakes, please take a look at the condition of the fish and any signs of Columnaris disease. Report any findings on the U of MN’s fish kill reporting map. The fish kill map is a tool created by Dr. Nick Phelps to identify fish kills in Minnesota and allows you to identify the date, location, approximate number of fish and other basic information of fish kills. UMN Staff then investigate the kill and may gather specimen samples for the UMN veterinary diagnostics laboratory.