New Zealand Mudsnail - Potamopyrgus antipodarum

Contact Information

Portland State University
Center for Lakes and Reservoirs
PO Box 751- ESR
Portland OR 97207-0751

New Zealand mudsnail, Potamopyrgus antipodarum, in Oregon

The New Zealand mudsnail, Potamopyrgus antipodarum, was first discovered in the Snake River, Idaho in the 1980s. It is now rapidly spreading throughout the western US and has become established in rivers, lakes and estuaries in 10 western states and three national parks. Mudsnails were first reported in Oregon, outside of the Snake River, in 1994 from Young's Bay Astoria.

The mudsnail is a parthenogenic livebearer with high reproductive potential - in other words it reproduces by cloning (most mudsnails in the West are genetically identical females), broods its young internally, and can reproduce relatively rapidly - often reaching densities greater than 100,000/m² in suitable habitat. Researchers in Montana report densities of this tiny snail (no longer than 5mm or less about 1/8 inch) approaching extremes of 750,000/m² in parts of Yellowstone National Park.

Due to this population growth mudsnails may comprise a significant proportion of the invertebrate biomass in invaded systems. Although limited research on mudsnails exists to date, decreases in native macroinvertebrate populations in several rivers have been documented. Mudsnails have also been shown to drastically alter primary production in some streams. As a result of these studies and the vast densities of mudsnails in Western rivers and streams this invasion has generated much concern about the potential effects it may have on native species, fisheries, and ecosystem health in the US.

Due to their small size, nondescript color and the ability to seal themselves up to avoid drying out, mudsnails can survive for days out of water and can be transported from location to location by unsuspecting boaters, anglers and other water users such as fish hatcheries, aquatic biologists, etc. Mudsnails may be transported in damp wading boots, poorly rinsed anchors and boat wells, nets and other gear. Because mudsnail transport is predominantly human driven it is imperative that water users and recreationists take great care to prevent further spread of these invasive species.

Individuals can help prevent expansion of the NZMS invasion by doing the following:

  • CLEAN and INSPECT - Thoroughly rinse and inspect all gear and
    boating equipment before you leave the area. Clean gear of all material coming
    from the water (ex: scrub soles of boots, rinse waders, drain cooling and livewell
    water away from shore) and inspect hard to clean areas like laces, insoles, etc.
  • DRY - Completely dry all gear and boating equipment for 48 hours before using
    in a different area. Multiple sets of gear are recommended for frequent travelers
    visiting many areas.
  • FREEZE, SOAK or SPRAY - Alternative cleaning methods include
    freezing gear overnight, soaking gear in hot water for 5 minutes (120F; warning,
    may damage Gortex), and applying Formula 409 Cleaner Degreaser Disinfectant Sol'n (50% dilution recommended) for 5 minutes (soak or shake in waterproof gear bag). Dispose of all chemicals and rinse water properly.
  • REMEMBER - Mud, sand, plant fragments and gravel on
    your gear are all signs that mudsnails may be hiding in your
    equipment (boots, nets, boats, trailers, etc.).
  • REPORT - To report a population of mudsnails or other invasive species
    please call 1-866-INVADER. Call is toll free in Oregon.

Mudsnails in the lower Deschutes system

deschutesOn Tuesday October 4, 2005 the Center for Lakes and Reservoirs confirmed the presence of New Zealand mudsnails (NZMS) in the lower Deschutes River. Following up on an anecdotal report of New Zealand mudsnails in the system, two Center for Lakes and Reservoirs employees, Laura Johnson and Steve Wells, passed out NZMS identification information and placed a NZMS sampling device at Heritage Landing at the mouth of the Deschutes River. A few days later, a Ranger Aide named Mark Ernes was talking to a boater and spotted the tiny snails in the runoff from the fellow's pressure washer. Earnes called the hotline and reported the snail.

.pdf of joint USFWS PSU press release here (61K)

Currently, mudsnails have been found in sparse populations along 90 river miles of the lower Deschutes River from Mecca Flats to Heritage Landing at the convergence of the Deschutes and the Columbia River. Mudsnails havebeen reported upstream of Lake Billy Chinook where the Crooked River enters Lake Billy Chinook.

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Continued spread of mudsnails along the Oregon Coast

Mudsnails have been present along the Oregon Coast since 1994 when they were first reported in the Columbia River estuary in Youngs Bay. In 1999 several snails were collected by Oregon DEQ near Gold Beach on the Rogue River and in 2003 a Zebra Mussel Monitoring Volunteer, Alice Pfand, reported mudsnails in Garrison Lake. By late 2004 mudsnails had also been reported in Devil's Lake (Lincoln City) and the New River/Floras Lake system. In 2005, thanks to heightened awareness of New Zealand mudsnails and information on how to identify these tiny invaders, mudsnails were reported from the lower Umpqua River and Coffenbery Lake. New locations continue to be reported. Please follow the link provided below for the most up-to-date information on mudsnail locations in Oregon.

Confirmed New Zealand mudnsnail locations in Oregon:

Up-to-date distribution maps from the USGS can be generated here.


all images by Robyn Draheim and are available for non-commercial use with citation

Call 1-866-INVADER or 1-866-468-2337 (tollfree in Oregon) or go to Oregon Invaders Hotline to report a new mudsnail sighting in Oregon.

To report a new location of a New Zealand mudsnail:

  • Collect a sample or take a picture (be sure to include an object for scale in your shot such as a coin, key or pencil). For New Zealand mudsnails we recommend that you collect 10-20 of the suspect snails and place them in a small jar filled with rubbing alcohol or place a few snails in a resealable sandwich bag with a cotton ball soaked in rubbing alcohol. It is important to take precautions when collecting a species you think is invasive. You must be certain that whatever you collect is unable to escape and infest a new watershed due to carelessness, improper containment or disposal. Upon calling with the following information we may ask you to send us the organisms you've collected.
  • Provide as much of the following information as possible. Here's what we'd like to know about your finding, the more details the better.
      1. State and County where collected.
      2. Water Body and Location: The name of the water body and the access point, something like "Deschutes River at Wapinita Campsite"
      3. Latitude and longitude: If you have access to a GPS unit, these can be decimal degrees, degrees and decimal minutes, or degrees, minutes and decimal seconds.
      4. Collection Date: The month, day and year. Time of day is also useful.
      5. Field Collector: The name of person or people who made the collection.
      6. Estimated Density: Select 1 of 3 crude levels (sparse, moderate or abundant).
      7. Comments: These might include notes on the species range up and down the river, whether or not collection was made at high or low tide, what you used to catch the species, exactly where you found the species, etc.

For more information

For more information on New Zealand mudsnails (or to report a location outside of Oregon) including how to identify mudsnails, current mudsnail distribution in the Western US, information on impacts and additional images please visit the USGS Nonindigenous Aquatic Species's mudsnail webpage [click here].