Isiah Holmes

The Department of Natural Resources (DNR) is investigating a fish kill which occurred in Isabelle Creek, in the  Pierce County community of Ellsworth. Several species of fish were observed in the fish kill, including more than 600 dead trout.

DNR staff have been onsite several times since Aug. 17. However, the investigation remains ongoing and no further details are available at this time, DNR representatives said. The creek flows for 13 miles, and connects to the Mississippi River at Bay City. According to the DNR, Isabelle Creek is a Class II Trout stream from its mouth to 7.6 miles upstream. Class II streams are regarded as valuable for spawning fish.

Nevertheless, in 2020 Isabelle Creek was noted as being in poor health. The creek’s headwaters were “not expected to support many bugs or fish,” the DNR reported, although  that portion of the stream wasn’t considered impaired.

The cause of a different fish die-off in the Fox River and Green Bay has been identified as a likely bacterial disease. Reports of dead fish began coming into the DNR on June 18, sparking a two week investigation. About 99% of the dead fish recovered by the DNR were channel catfish, though carp and sheepshead were also found. Just four of the dead catfish that were recovered were suitable for testing.

“Despite almost two weeks of responding to public reports and searching, it was difficult to find either sick or freshly dead fish suitable for testing. Most of the fish seen had been dead for at least a day,” said Dave Boyarski, DNR East District Fisheries Supervisor. “Once a fish dies, they start to decompose and can quickly become unsuitable for testing, especially if the water is warm.”

Most of the dead fish were found downstream of the De Pere Dam, and in lower Green Bay. Some fish were found as far north as Sturgeon Bay and upstream of the Fox River near Wrightstown, however. It’s unknown where the fish came from.

The bacterial infection was identified as columnaris, a common bacterial disease in freshwater fish. It causes yellow-bown or white lesions on the skin, fins, and gills of fish. Outbreaks of columnaris are normal in late spring and early summer, when the warm is warming up, according to the DNR.

“It is unusual to see a large die-off of wild, adult channel catfish, but they are known to be susceptible to columnaris,” said Nicole Nietlisbach, DNR Aquatic Veterinarian. “It is possible that warm weather and high levels of organic matter in the water from recent rainstorm runoff created a very favorable environment for Flavobacterium columnare growth during the catfish spawning season, which is an already stressful time for the channel catfish.”

Wisconsinites are encouraged to report any and all fish die-offs to the DNR. Columnaris bacteria does not infect humans or other animals, and water quality testing in the areas where the die-offs occurred were normal.

This story was written by Isiah Holmes, a Wisconsin-based journalist, where this story first appeared.