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New Zealand Mudsnail

New Zealand MudsnailSpecies and Origin

A tiny snail that reproduces asexually. Native to New Zealand, it was accidentally introduced with imported rainbow trout in Idaho in the 1980s and into the Great Lakes via ballast water from ocean going ships.


Densities can reach 100,000 to 700,000 per square meter. They outcompete species that are important forage for native trout and other fishes and provide little nutrition to fish that eat them.


First discovered in the late 1980s in the Snake, Idaho, and Madison Rivers, they quickly spread to other western rivers. They were discovered in Lake Ontario, and later in Thunder Bay, Lake Superior in 2001. In fall of 2005, they were discovered in the Duluth-Superior harbor.

Where to Look

Look on docks, rocks, and other hard surfaces along the shorelines and bottoms of lakes, rivers, and streams.

Regulatory Classification

It is proposed as a prohibited invasive species (DNR), which means import, possession, transport, and introduction into the wild will be prohibited.

Means of Spread

They likely spread by attaching to recreational fishing gear, other types of equipment placed in the water, or in fish shipments.

How Can You Help?

  • Inspect and remove visible animals, plants, and mud from waders, recreational fishing equipment, research gear, and other field equipment.
  • Rinse everything with 120° F water, or dry equipment for 5 days.
  • Report suspected infestations.

(Information provided by the Minnesota Department of Natural Resources)