Potamopyrgus antipodarum. (New Zealand mudsnail)

Animal Molluscs
Family: Gastropoda
Classification: Prohibited

New Zealand Mudsnail
Mudsnail ID card - USFWS
New Zealand Mudsnail fact sheet
Fact Sheet

New Zealand mudsnails are tiny non-native snails that have infested an increasing number of Washington's lakes and streams. These snails multiply quickly and disrupt the food chain, threatening native fish. The species' size makes it easy for anglers and boaters unknowingly to transport mudsnails from one waterbody to another. To date, there is no way to eradicate mudsnails once they have infested a waterbody without damaging the aquatic habitat.


New Zealand mudsnails are small (an average of 1/8 inches long) and cone-shaped. Their shells have five to six whorls, fairly uniform in size, and vary in color from light-brown to black.

This species of mudsnail is hearty, surviving in a variety of salinity, water temperature and quality.  A movable cover at the opening of its shell (the "operculum") allows the mudsnail to protect itself from short-term exposure to most chemicals. The New Zealand mudsnail also survives out of water for quite some time and has no known predators or parasites in Washington state that can keep populations in check.

A single female snail can rapidly reproduce through cloning, adding 230 snails to the population annually. That initial snail, along with its offspring, can build a population into the billions of snails within a four-year timeframe.

New Zealand mudsnails mostly feed at night on algae, sediment, plant and animal detritus – all of which would otherwise be consumed by native snails and insects.

Potential Risks

New Zealand mudsnails pose both an ecological and an economic threat to Washington state. These mudsnails can quickly dominate river and lakebed habitat. Thanks to rapid self-reproduction, the species can quickly achieve densities of more than 500,000 snails per square meter. After moving into a lake or stream, mudsnails are nearly impossible to remove without damaging other aspects of the habitat. 

New Zealand mudsnails compete with other native species for food, disrupting the food chain. Ultimately, native fish species, such as steelhead and salmon, could be affected. This would disrupt the state's efforts to recover federally threatened species and put at risk Washington's fishing industry.

History and locations in Washington

New Zealand mudsnails were found in 1996 near the mouth of the Columbia River.  By early 2014, the species had spread to more than a dozen sites across Washington (see map).

The species has invaded waterbodies as far north as Union Slough on the Snohomish River and inhabit several locations along the Columbia River, including around the Hanford Reach area. Infestations have been confirmed in popular lakes such as Lake Washington and Olympia's Capitol Lake as well as in Grays River and Blue Slough on the Chehalis River.

Not native to the United States, New Zealand mudsnails were spotted initially in this country in 1987 in Idaho's Snake River.  The species is now widespread throughout the West, including in Yellowstone National Park, American River in California and parts of Lake Powell in Arizona. New Zealand mudsnails also have spread east to the Great Lakes and the St. Lawrence River.


Boaters, kayakers, anglers and anyone who recreates or works in Washington's waters should take measures to help prevent the spread of New Zealand mudsnails.

For more details on the prevention methods, visit WDFW's webpage on preventing the spread of aquatic invasive species.

Report new infestations

If you observe New Zealand mudsnails or any other known or suspected aquatic invasive species in a previously unreported waterbody, please report the sighting to WDFW.

Find the waterbodies where mudsnails have been reported on this website:

Report new sightings here: http://wdfw.wa.gov/ais/reporting/


Legal Classification

New Zealand Mudsnails are classified as "Prohibited level 3" species under RCW 77.135.030(1)(c) for species considered to pose a "moderate to high invasive risk" and which may require management by the department or other affected landowner. Prohibited level 3 species, under RCW 77.135.040(1), "may not be possessed, introduced on or into a water body or property, or trafficked, without department authorization, a permit, or as otherwise provided by rule."