OSHKOSH – Initial lab tests on dead fish found in Lake Winnebago indicate a probable outbreak of VHS, a virus that affects a wide range of fish species. The virus is not known to be harmful to humans.
Based on current observations, fisheries biologists do not expect this die-off, which is primarily affecting fresh water drum, to have a significant effect on the Winnebago fishery.
VHS refers to viral hemorrhagic septicemia virus. It can affect as many as 50 species of freshwater and marine fish. Multiple strains occur in different regions of the world and affect various species differently. The late winter and recent weather created conditions favorable for the virus. VHS has been detected in lakes Michigan and Winnebago for more than a decade.
“This outbreak on Winnebago serves as a stark reminder to all anglers about the critical importance of disinfecting boats and gear when moving between bodies of water,” said Kendall Kamke, fisheries team supervisor for the Department of Natural Resources at Oshkosh.
Guidelines for preventing the spread of invasive species and pathogens require that boaters do not transfer water, fish or vegetation from one body of water to another. More information on this is available at https://dnr.wi.gov/topic/Invasives/boat.html.
DNR fisheries biologist Adeline Dutton initially responded to reports of dead fish in the Fond du Lac area on April 24. Dutton found hundreds of dead fish, most of them freshwater drum, also known as sheepshead, as well as common carp, black crappie, yellow perch, largemouth bass and bluegill.
Dutton's samples included five sheepshead, three black crappies, and one each of perch, bluegill and largemouth bass. These were processed by DNR fish health specialists and then sent to the La Crosse Fish Health Center, a laboratory operated by the U.S. Fish & Wildlife Service.
Previously, on April 23, an industrial fire at AP Nonweiler in Oshkosh caused the release of a non-toxic white substance – titanium dioxide mixed with fire-fighting water – that was highly visible in a channel to Lake Winnebago that Monday evening. At the same time, decaying blue-green algae, also white, was seen along the west shore of Lake Winnebago.
DNR biologists believe there is no connection between these two events and the dead fish. DNR issued a news release to this effect on April 25.
DNR crews conducting fish surveys reported seeing large numbers of dead sheepshead near shore and out in the open water of Lake Winnebago. On Monday, April 30, DNR staff collected 43 sheepshead and four black crappie from the area of South Asylum Bay near Oshkosh and another 10 sheepshead from the harbor at High Cliff State Park on the northeast side of the lake. All these fish were recently dead or dying. They were taken immediately to the USFWS lab in La Crosse.
On Wednesday, DNR learned the samples collected near Fond du Lac tested positive for VHS. These are initial results. The lab is also searching for other potential pathogens. The full lab report will be available in about four weeks. The DNR investigation into the fish die-off is continuing.