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An invasive snail has been found in Black Earth Creek that experts say has the potential to disrupt one of the state’s best trout fishing destinations and quickly spread to other area streams and rivers.

A large number of tiny New Zealand mudsnails were discovered in the stream by South Valley Road in western Dane County about a month ago, said Susan Graham, the lakes management coordinator for the state Department of Natural Resources.

Mudsnails could affect the size, quality and number of trout in Black Earth Creek, Graham said. Although they grow to just one-eighth of an inch, the snails can create ecological havoc in trout streams because densities of the creatures can reach more than 500,000 per meter and starve out native prey that the fish eat.

“That’s our greatest fear,” Graham added.

It marked the first time the snail has been found in an inland Midwest waterway, she said. The snail has been a menace to streams and rivers in western U.S. since the late 1980s and was found in the Great Lakes about 20 years ago. The invasion is irreversible.

“We all got super depressed when we first heard about them. It was just like, ‘Oh man, this is a bad one,’ ” Graham said. “This isn’t just some little thing we can eradicate and work on. Once we have it, we have it.”

An informational meeting that will focus partly on keeping the snail from spreading to other streams will be held 7 p.m. Thursday at the American Legion Hall in Cross Plains. Representatives from the DNR, UW-Extension and the River Alliance of Wisconsin will be there.

Edward Levri, a mudsnail expert from central Pennsylvania, doesn’t think the snail can be stopped from spreading to other area streams and rivers. Levri said Black Earth Creek is heavily traversed by anglers, hunters, trappers and others. And the snails can survive out of the water for nearly a month on fishing equipment, on the sole of a boot or on clothing, he said.

“I suspect it’s going to spread very rapidly throughout the entire region,” said Levri, a biology professor from Penn State Altoona who co-authored a report on an outbreak of mudsnails in the Lake Ontario watershed in 2008.

Graham said bleach and alcohol don’t affect snails, but they can be killed by freezing. “At this time of year, it’s a great method. We’re asking the public to freeze their gear before they move to another body of water,” Graham said.

All of the mudsnails in the United States are asexual; just one can essentially clone itself into a colony of millions in one year. There are at least three clone types of mudsnails. The one identified by the DNR that was found in the Black Earth Creek — called U.S. 1 — has created the most problems in terms of density, Levri said.

In Wyoming’s Green River, trout forced to feed on the mudsnails decreased in size and number because they are such a poor food source, according to a report by from Utah State University and the U.S. Bureau of Land Management.

“But in other locations it doesn’t seem to have much of an effect at all,” Levri said.

Some researchers believe the science of Midwest streams could lead to a stronger proliferation of the snails than in western states and Australia. For instance, Black Earth Creek is mostly spring fed, which is favored by the snails.

“I would suspect, especially in a high quality trout stream, that you would get pretty high densities in the order of several thousand per square meter,” Levri said. “So I suspect it will have some impact. It will compete with some native species. It might affect some of the nutrient cycling going on.”

Controlling the spread of the invasive species should be the biggest concern right now, Levri said. He told a story about how a colleague spotted the snails on the bottom of an aquarium in a pet store in Iowa.

“If they are already in the pet trade, they are going to be everywhere before we know it,” Levri said.

So that means special precautions must be taken by anglers and everyone else who enjoys Black Earth Creek. Jeff Smith, the legislation committee chair for Wisconsin Trout Unlimited, said he is giving up wearing waders when he fishes there from now on.

Speaking for all anglers, Smith said, “We’re not real happy about this.”

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Rob Schultz has won multiple writing awards at the state and national levels and covers an array of topics for the Wisconsin State Journal in south-central and southwestern Wisconsin.