New Zealand Mud Snail

Two small shells sit on a dime
New Zealand mud snails shells on a dime.



The New Zealand mud snail (Potamopyrgus antipodarum) is an invasive species that became established in the western United States since the 1980s. In suitable habitat, especially in geothermal streams with high primary production, it can form dense colonies on aquatic vegetation and rocks along streambeds, crowding out insect communities—a primary food for immature trout and other native species.

New Zealand mud snails consume a large amount of algae, which is a primary food for native aquatic invertebrates. Its overall impact on algae is likely to affect entire stream food webs. With its protective shell, the mud snail provides little if any nutrition as prey and may pass through a fish alive. Scarcely a quarter-inch long, mud snails may cling to boats, waders, and other fishing gear by which they are inadvertently transferred to another watershed. Because the species can reproduce asexually, a single mud snail is all that is required to establish a new colony.


First detected in the park in 1994, New Zealand mud snails are now in all of the major watersheds. Although the mud snail is abundant in several streams, it remains absent or uncommon in other Greater Yellowstone streams, suggesting that its upstream population density and distribution is limited by colder temperatures, low productivity, and unstable substrates associated with spring runoff.

Impacts of Mud Snails

Once mud snail colonies become established in a stream, removing them without disrupting native invertebrate populations is not feasible with any known method. Mud snail research in Greater Yellowstone aims to determine the species’ impacts on other aquatic organisms and stream ecology. A study of the Gibbon and Madison rivers found that 25–50% of the macroinvertebrates were mud snails, and the areas they occupied had fewer native mayflies, stoneflies, and caddisflies—insects important in the diet of salmonids and several bird species.

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Whirling disease can infect some trout and salmon.

Brightly-clothed people in a river near a steaming thermal feature

Red-rimmed Melania

Red-rimmed melania, a small snail, was discovered in a warm swimming area.

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Lake Trout

Lake trout prey on Yellowstone cutthroat trout.

Rainbow trout in the hands of an angler

Rainbow Trout

Rainbow trout are native to North America in waters which drain to the Pacific Ocean from northern Mexico to Alaska.

Eastern brook trout swimming

Eastern Brook Trout

Eastern brook trout was the first nonnative species introduced in Yellowstone—stocked in the (then fishless) Firehole River in 1889.

Head and body of a brown trout laying on the ground

Brown Trout

The brown trout is the only nonnative fish species in Yellowstone that is not native to North America.

Lake chub held in hand

Lake Chub

Native to the Missouri and Yellowstone river drainages in Montana and Wyoming, the lake chub is not native to Yellowstone National Park.

Angler fishing in Yellowstone during a golden morning.

Catch a Fish

Be a responsible angler and understand the regulations before you come.

Photo of a park employee cleaning a boat with a power washer.

Clean, Drain, and Dry

Protect park waters by preventing the spread of aquatic invasive species.

striped mussels in a tight group

Aquatic Invasive Species

Aquatic invasive species can disrupt ecological processes.

Young cutthroat trout swimming in shallow water

Native Fish Conservation Program

Learn how the Native Fish Conservation Program works to preserve Yellowstone Lake cutthroat trout and to restore fluvial trout populations.

An underwater view of a spotted fish with a red slash on its neck and side swims above pebbles

Native Fish Species

Native fish underpin natural food webs and have great local economic significance.

Fisheries staff member holds a 36-pound spawning lake trout removed from Yellowstone Lake.

Nonnative Fish

Lake trout and other invasive species pose many threats to Yellowstone's aquatic ecosystem.

Last updated: November 5, 2019

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