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Koi herpes virus blamed for dead carp in Madison lakes and the Yahara River, DNR says

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Koi herpes virus killing carp in Madison lakes

About two dozen carp killed by a weakened immune system from the Koi herpes virus line the northeastern shore of Lake Monona Tuesday. They washed ashore in recent days and were gathered up by a nearby condominium resident.

Dead carp washing up on the shores of Madison lakes and rivers recently were likely killed by a virus that has been found in area waterways for the first time.

The Wisconsin Department of Natural Resources said Wednesday that dead carp found in Lake Kegonsa in August tested positive for the koi herpes virus. The virus likely killed carp recently found decaying along the shoreline of lakes Monona and Waubesa and the Yahara River, according to the DNR.

While the koi herpes virus can’t be passed to humans or other animals, DNR fisheries biologist Dan Oele recommended avoiding direct contact with dead carp.

“The public is not at risk from the koi herpes virus, and sport fish and forage fish such as shiners have not been harmed,” he said.

Although the virus can’t be transmitted to humans, decomposing carp can harbor other harmful bacteria.

The virus weakens the immune systems of the invasive species, making them vulnerable to other infections, according to the DNR.

Carp die-offs may continue until water temperatures begin to cool, Oele said. The virus is deadliest when the water is between 71 and 79 degrees.

The virus was first found in Wisconsin in the Rock River near Horicon in 2014, Oele said.

After the 2014 Rock River die-off, the carp population rebounded, and there has been no evidence of another virus-related die-off, he said.

“They are tough critters,” Oele said.

The virus’ existence in other states has been linked to the release of ornamental koi fish, the DNR said in 2014.

Oele said fisheries personnel don’t have a hard count, but in each of the three lakes they estimate that hundreds to thousands of carp have died since reports started coming in around Aug. 14.

Madison’s Clean Lake Alliance has heard reports of an unusual number of dead carp in lakes Monona and Mendota and the section of the Yahara River that connects the two since early last week, said Paul Dearlove, watershed program director for the alliance.

About two dozen foul-smelling, decomposing carp lined the shore of Lake Monona earlier this week at the end of Ferchland Place in Monona. A lakeside condominium resident had been gathering most of the dead carp on the lake shore along her residence and placing them there for the last week.

Dead carp can be buried, put in garbage bins, composted, placed in landfills or used as farm field fertilizer, according to the DNR. In most cases, it is up to property owners to dispose of the dead fish.

“Unfortunately, from the property owners’ perspective, it’s their responsibility … to remove and dispose of those carcasses,” Dearlove said. “It’s a nasty job.”

Unlike past efforts to cull the sediment-churning species in area lakes, like Wingra and Kegnosa, the virus likely won’t significantly impact the carp population, he said.

“Since it’s such a minor die-off, it’s probably not even putting a dent in the population,” Dearlove said.

State Journal reporter Steve Verburg contributed to this report.

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Related to this story

DNR officials confirmed koi herpes virus is responsible for a carp die-off reported July 21 in Horicon Marsh and Lake Sinissippi and suspect it to be the cause of a July 31 die-off in Silver Creek, a Rock River tributary in Watertown.

Friends of Lake Kegonsa, a group of homeowners, businesses and lake users, plan to radio tracking data from a group of carp to assist an expensive eradication project that could remove a million pounds of fish from the lake.

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