New Zealand mudnsails

New Zealand mudsnails are the size of a grain of sand, between 4-6 mm.

The first confirmed invasive mudsnail infestation in the Rock River Watershed has been found in the Oregon branch of Badfish Creek.

The New Zealand mudsnail is an incredibly small freshwater gastropod mollusk that can reach extremely large densities and disrupt native plant and fish species. The snails grow up to only 6 mm in length and reproduce asexually – a single snail can result in a colony of over 40 million in just one year. There are no predators in their native range and there is no evidence that predators do or could control populations in Wisconsin, according to a news release from the Wisconsin Department of Natural Resources.

The snails are classified as an “NR40 prohibited invasive species,” meaning they can cause harm to the environment, human health or the economy by choking out native species of fish by depriving them of their preferred food. Because of the lack of research, it’s uncertain what impacts the species will have on Wisconsin streams, according to the news release.

The discovery, just east of Oregon, is the sixth inland stream where the snails are known to be located in the state. They were also found in Brewery Creek, a tributary to Black Earth Creek in Cross Plain. The snails were found in Black Earth Creek in 2013 and have since spread to Milwaukee Harbor and Rowan, Badger Mill and Mount Vernon creeks.

Due to the snails’ tiny size and “stickiness” to boots and other surfaces, as well as the ability to survive out of water for “a long time,” the DNR recommends special precautions to prevent transferring the snail to new water systems. A brush to scrub boots and waders is strongly encouraged – those are sometimes available for use at kiosks at popular trout fishing access points.

Equipment can also be thoroughly rinsed with tap water after scrubbing, but that should be done only away from streams or bodies of water. Gear can also be frozen for at least eight hours.

Gear decontamination research is ongoing. Check with state resource agencies and conservation groups for new methods as they become available.

For more information about the invasive and DNR efforts, and search “New Zealand mudsnail.”

Contact Amber Levenhagen at

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