A virus that first appeared in Wisconsin waters in 2014 and affects common carp and koi is the likely cause of carp die-offs in Madison lakes this past month.

Department of Natural Resources officials say the koi herpesvirus first appeared in Lake Kegonsa around August 11. Testing confirmed the presence of the virus, which appears to have spread to lakes Waubesa and Monona through the Yahara River system.

“The public is not at risk from the koi herpesvirus, and sport fish and forage fish such as shiners have not been harmed,” said DNR Fisheries Biologist Dan Oele.

“However, DNR encourages use of protective clothing such as gloves in removing the dead carp due to other bacteria the fish may be hosting.”

Oele said property owners are encouraged to remove fish carcasses that might accumulate on their property, which can be put in a dumpster, composted or buried for disposal.

Boaters should always:

  • Inspect boats, trailers and all  equipment.
  • Remove all attached aquatic plants and animals.
  • Drain all water from boats, vehicles and equipment.
  • Never move plants or live fish away from a water-body.
  • These steps will help reduce the spread of any fish diseases or invasive aquatic plants.
  • Use soapy water to wash and then thoroughly dry any gear or nests that may have come in contact with an infected fish.

Koi herpesvirus first appeared in Wisconsin in 2014 in the Rock River near Horicon, and caused a carp die-off along the river and Lake Koshkonong. The virus is transmitted through waterborne contact with the gills and skin and it can survive outside of fish for up to seven days.

Additional carp die-offs may occur until water temperatures begin to cool with the onset of fall. Mortality rates of carp infected with koi herpes virus are greatest when water temperatures are between 71 and 79 degrees Fahrenheit. There is no treatment available to control the virus in wild fish.

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