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Rock River carp virus to hit Janesville, Beloit in a few weeks

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Andrea Behling
August 27, 2014

NEWVILLE—The koi herpes virus expected to leave thousands of dead carp littering hundreds of miles of the Rock River has arrived in Lake Koshkonong, a state fisheries biologist said.

The die-off started in the headwaters of the Rock River near Horicon Marsh in mid July, reached Lake Koshkonong late last week and likely will be in Janesville and Beloit in two or three weeks, state Department of Natural Resources fisheries biologist Laura Stremick-Thompson said.

The virus is the carp equivalent of Ebola with a mortality up to 80 percent, Stremick-Thompson has said.

Property owners have reported hundreds of dead fish downstream of Lake Koshkonong and upstream of the Indianford Dam, Stremick-Thompson said.

A Rock-Koshkonong Lake District resident said he's picked up about 30 dead carp between 4 and 12 pounds along the north side of Bingham Point on the Lake Koshkonong shoreline.

The Rock River for another three weeks will be at 71 to 79 degrees—the temperature at which transmission is most pronounced, Stremick-Thompson has told The Gazette.

The virus affects only koi, which includes common carp, and was likely brought to the Rock River by a “phantom stocker” who didn't want to feed fish in a koi pond anymore and decided to free the fish, Stremick-Thompson has said.

It's the first time the koi herpes virus has been reported in Wisconsin waters, Stremick-Thompson said.

Rock-Koshkonong Lake District Chairman Brian Christianson said the DNR has been “pretty clear of responsibilities” for cleaning up the dead fish.

Stremick-Thompson said the DNR is not able to offer cleanup for a naturally induced fish kill.

“Given the size, it's just not feasible,” Stremick-Thompson said.

Property owners along the water are allowed to clean up the dead fish, but officials said the DNR, the lake district and Rock County Health Department are not responsible for cleanup.

Dead fish could bring hundreds of birds to the riverbanks, and the offensive smell could deter recreational water use, Rock County Health Department Director Tim Banwell said. The dead carp will take oxygen out of the water, which could affect other species, Banwell said.

While the smell and sight of decomposing carp isn't pleasant, the die-off isn't all bad news, Christianson said.

Carp compete with game fish and damage wetlands that haven't been protected, Christianson said.

“Hopefully, this virus will take a really large bite out of the carp population. They're very destructive to the overall habitat,” he said.

Jason Dillon, who has a contract to harvest carp from Lake Koshkonong, estimated 4 million to 8 million pounds of carp swim in the lake with an average carp weighing 7 or 8 pounds.

Now that the virus has been introduced to Wisconsin waters, it's here to stay, Stremick-Thompson said.

The carp population will be knocked significantly from the initial outbreak, but the virus is not a “silver bullet” for getting rid of the rough fish, she said. Some fish will survive, produce antibodies to fight the virus and reproduce, Stremick-Thompson said.

“It's not going to kill all the carp. It's really just creating a very bad situation for our recreational water users,” she said.

Stremick-Thompson predicts future outbreaks will not be as severe because survivors will have built up immunity to the virus.



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