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Sometimes nature stinks: Fish deaths on Detroit Lake due to natural causes

It may not be pretty, but it's normal. Fish dying from Columnaris Disease happens every year, but this year it is more pronounced due to the rapid rise in water temperature from the late ice off-quick warm up. (Paula Quam / Tribune)

Detroit Lakes city staff has received several calls and other inquiries regarding dead fish washing ashore on Little and Big Detroit Lakes.

The likely cause is a naturally-occurring bacteria called Columnaris Disease, according to Paul Diedrich of the DNR Fisheries Division.

This year's effect is especially pronounced due to the rapid rise in water temperatures, he said. A late ice-off combined with unseasonably hot weather has impacted the water temperature in area lakes, but fortunately the impacts of the spring die-off are generally short-lived.

In the meantime, the City Parks Department continues to do a daily cleaning of the City Beach, picking up dead fish, weeds and trash and disposing of it in the garbage, said Detroit Lakes Public Works Director Brad Green.

The campaign against flowering rush has been successful and the city's mile-long beach is popular again, so park department workers often start their day at 5 a.m. making a clean sweep of the beach, Green said.

"It's a 3,100 acre natural lake, there are going to be fish floating around out there, it's part of nature," he said. "But we take care of our beaches, we keep them in the best shape we can."

The south wind over the last week resulted in a direct impact to the City Beach, so the fish kill was very noticeable over the weekend, and there were complaints.

Green said the city remains committed to maintaining the Mile Long Beach so it is an attraction to residents and visitors alike.

According to Paul Diedrich, DNR Fisheries, Columnaris disease is a common cause of fish deaths.

The disease is caused by a bacterium called Chondrococcus columnaris. The bacterium is always present in fish populations, but seems to affect fish most in spring, when most of the die-offs occur. It is in spring when water temperatures are warming and fish are undergoing some stress due to spawning.

Sometimes, thousands of fish are observed dead or weakly swimming along shores that are windswept. Species affected are usually sunfish, crappies and bullheads and occasionally, largemouth bass and northern pike.

When a die-off occurs it is usually a small percentage of the populations that are affected and fishing success is not influenced.

Symptoms of the disease are discolored patches on the body, sloughing of scales, eroded gill filaments and high mortality. It is recommended that fish dead or dying due to Columnaris disease not be consumed. However, any game fish caught which are normal in appearance and behavior from the same lake may be consumed.

There is no practical cure for Columnaris disease as it occurs in the wild. Fish kills due to Columnaris can be quite widespread in this area. Usually kills on a dozen or so lakes are significant enough so as to be reported by the public each year. During the hot, droughty years of 1987-88, Columnaris disease killed fish on virtually every lake in the management area.

Sometimes when fish kills happen, people are quite concerned that something may be poisoning the environment. Columnaris disease is generally not a result of man's activities on the environment, Diedrich said.

"We do appreciate it when the public reports fish kills, and we will conduct an investigation if that appears warranted," he added. "The DNR biology laboratory in St. Paul has a limited ability to receive specimens delivered from our office or the general public."

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