Iowa Department of Natural Resources Fisheries biologist, Ben Wallace, says testing at Storm Lake has confirmed the disease that killed thousands of fish.

“It’s the Koi Herpes Virus. It’s a virus that specifically affects common carp. And then kind of their ornamental counterpart, which are Koi. Koi-R carp it’s the same species, you know, they just kind of been selectively bred over time for their colors,” he says.

He says this is the first known outbreak in an Iowa lake. Wallace says they can’t say for sure how the virus got into the lake.
“We do know that it’s spread through like direct social contact amongst these fish. So it’s not likely that it would have been transferred in water, you know, like somebody’s bilge or live well, or anything like that,” Wallace says. “So, with that in mind, it’s quite possible that these fish could have had this disease for generations upon generations, since they were first introduced in Storm Lake. And just something happened now that kind of allowed this virus to manifest itself.”

Wallace says the heat and spawning were likely contributing factors that made the virus worse. Removing carp can help improve water quality — but Wallace says this outbreak only killed young fish in the same year of growth. “Now it is hitting that year class pretty hard — but there’s a lot of other cars out there. And there’s a lot of adults out there that will be able to reproduce next year,” he says. “My guess is, you know, if anything, we may see a little bit of a short-term improvement water quality, if enough of them died, but it’s not likely that we’ll see any sort of benefit in the long term.”

He says these type of carp kills have happened at many lakes in Minnesota, and Wisconsin, but there’s no way to know if it will happen again here. “It’s possible but impossible to predict. You know, this stuff actually been researched quite a bit. even looked at as a tool for carp management, and it’s just not reliable, there’s no way to kind of trigger an outbreak, you know, when you want to,” according to Wallace. He says it takes a lot of conditions to come together to cause the problem in the fish who carry the virus. “We may see it again soon or we may not see it for another 50 years,” he says.

Wallace says the fish are decomposing pretty quickly and scavengers, like raccoons, catfish and crayfish are also eating away at the fish.