Aquatic Invasive Species

Whirling disease discovered in Yellowstone, Lewis, Firehole Rivers, Pelican & Clear Creeks. New Zealand mud snails have been discovered in Lewis, Madison, Firehole, Gibbon & Yellowstone Rivers, Nez Perce Creek. Red-rimmed melania in Gardiner River.
Locations in Yellowstone National Park where whirling disease, New Zealand mud snails, or red-rimmed melania have been documented.

An aquatic invasive species disrupts ecological processes because it is not indigenous to the ecosystem. Invasive organisms can cause species extinction, with the highest extinction rates occurring in freshwater environments. In addition to nonnative fish in Yellowstone, three aquatic invasive species are having a significant detrimental effect:

  • Myxobolus cerebralis, a parasite that causes whirling disease in cutthroat trout and other species.
  • New Zealand mud snails (Potamopyrgus antipodarum), which form dense colonies and compete with native species; and
  • Red-rimmed melania (Melanoides tuberculatus), a small snail imported by the aquarium trade starting in the 1930s, was discovered in the warm swimming area at the confluence of the Boiling River with the Gardner River in 2009.

Smallmouth bass (Micropterus dolomieu) was captured by an angler outside the park, in the Yellowstone River just downstream of the Gardner River confluence, in February 2022. Smallmouth bass have been shown to greatly reduce populations of native trout when they invade an area. Subsequent eDNA surveys of the area did not detect any further smallmouth bass DNA in the water.

Preventing the arrival of additional aquatic invasive species is critical because eliminating them after they become established in a watershed is usually impossible and efforts to reduce their impact can be extremely expensive. Each summer a small team of park technicians inspect the crafts brought in by park visitors before they put their boats or angling gear in the water. They inspect visitor’s equipment and decontaminate it, if necessary. Such decontamination is usually adequate to prevent the entry of most aquatic invasive species.


Arrival in Yellowstone

During the late 1880s when the Army administered Yellowstone, the US Fish Commission (a predecessor of today’s US Fish and Wildlife Service) stocked nonnative fish in some park waters. These stockings comprise the first known, deliberate introductions of nonnative fish to Yellowstone. Four trout species were widely introduced—brook, brown, lake, and rainbow. Rainbow trout hybridize with native cutthroat trout, thus diluting genetic diversity. All four compete with and prey upon native fish.

Other aquatic invasive species, such as the New Zealand mud snail and the parasite causing whirling disease, probably arrived via unaware visitors and anglers carrying the organisms from other locations around the country. We may never know exactly how those species were introduced to the park, but anglers can help prevent other species from arriving.

Two shells sit on a dime and are about the same height as the coin
New Zealand Mud Snails

New Zealand mudsnails are invasive and have a significant detrimental effect on Yellowstone.

Two speckled fish with black tails swim in a colorful streambed
Whirling Disease

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.


Incoming Threats

The aquatic invasive species which pose the greatest risk to ecologic, recreational, and economic values in the Yellowstone area include zebra and quagga mussels, Asian clams, Asian carp species, Eurasian watermilfoil, hydrilla, flowering rush, and viral hemorrhagic septicemia. Fisheries biologists believe several of these species are moving toward Yellowstone.

Their arrival might be avoided if anglers remember:

  • Remove all plants, animals, mud, sand, and other debris from your boat, boots, and equipment.
  • Do not dump water or organisms from other sources into Yellowstone waters.
  • Drain your boat bilge area, live well, and other compartments away from all waters.
  • Dry all equipment in the sun for 5 days or use high-pressure, hot (>140°F) water to clean your boat, trailer, waders, boots, and equipment.

Zebra mussels (Dreissena polymorpha) and closely related quagga mussels (Dreissena bugensis), collectively called dreissenids, are of particular concern given their ability to attach to watercraft, survive many days out of water, and cause irreparable harm.

Zebra mussels are native to Eastern Europe and western Asia. They were first discovered in North America in 1988 in Lake St. Clair, one of the water bodies connecting the Great Lakes. It is believed that this invasive species was introduced through ballast water discharges from international shipping.

Following their initial invasion, zebra mussels spread quickly across most of the eastern United States and Canada. Zebra mussels are inadvertently transported to new water bodies by boaters who trailer their boats between infected bodies of water.

Zebra mussels drastically alter the ecology of infested water bodies and may severely impact ecosystems. Once established, these efficient filter-feeders consume significant biomass of phytoplankton, depleting the foundation of the aquatic food web. Zebra mussels can attach to most hard surfaces, forming mats that may be up to 18 inches thick. Mussels can impact recreation activities and associated economies by covering docks, boats, and beaches; in addition to causing severe infrastructure and economic damage by blocking water supply pipes of power and water treatment plants, irrigation systems, and industrial facilities.

Zebra mussels’ native predators from Europe, certain types of birds and fish, are not present in North America. Though some

The bighead carp (Hypophthalmichthys nobilis), black carp (Mylopharyngodon piceus), and silver carp (Hypophthalmichthys molitrix) occur in at least 24 states. They out-compete native fish, reduce forage for other fish, and can transmit disease. Silver carp are also known for their ability to jump great distances out of the water when boats travel near them, causing injury to boaters.

Silver carp are native to Southeast Asia and east Russia and were intentionally introduced into the United States in 1973 in an attempt to improve water quality, increase fish production in culture ponds, as biological control and as food fish. Silver carp now occurs in at least 24 states and is naturally reproducing. Both the silver and the bighead carp compete for food (zooplankton) with native fish.

Black carp are native to Asia and eastern Russia. These fish were unintentionally introduced as a stowaway with intentionally introduced grass carp. Black carp now occur in at least nine states. Black carp may reduce populations of native mussels and snails through predation and negatively affect the aquatic ecosystem. None of these species are currently found in Wyoming, or Montana.

These invasive species may continue to be spread intentionally or through accidental introductions through improper use and disposal of live bait as fish or fish eggs and through connected waterways.

Since the introduction of Corbicula fluminea to the United States in 1938, it has spread into many of the major waterways and is now found in 46 of the states. The species have not been completely distinguished, but most varieties are small light-colored bivalves, yellow-green to light brown in color.

The native ranges are in temperate to tropical southern Asia west to the eastern Mediterranean; Africa, except in the Sahara desert; and southeast Asian islands south into central and eastern Australia. The Asian clam is a filter feeder that removes particles from the water column. It can be found at the sediment surface or slightly buried. Its ability to reproduce rapidly, coupled with low tolerance of cold temperatures (2-30°C), can produce wild swings in population sizes from year to year in northern water bodies.

Eurasian watermilfoil (Myriophyllum spicatum) has spread to all of the United States except Hawaii and Wyoming. In 2007, it was found in Montana.

This nonnative aquatic plant lives in calm waters such as lakes, ponds, and calm areas of rivers and streams. It grows especially well in water that experiences disturbances, sewage spills or abundant motorboat use, such as Bridge Bay.

Eurasian water-milfoil colonizes via stem fragments carried on boating and angling equipment, emphasizing why boats, equipment, and trailers should be thoroughly cleaned, rinsed, and inspected before entering Yellowstone National Park.

Three nonnative plankton species which can displace the native zooplankton that are important food for cutthroat trout may be on their way. These nonnative zooplankton have long spines, which make them difficult for young fish to eat.


The Yellowstone Resources and Issues Handbook, updated annually, is the book our rangers use to answer many basic park questions.

Bartholomew, J.L. and P.W. Reno. 2002. The history and dissemination of whirling disease. In J.L. Bartholomew and J. C. Wilson, ed., Whirling disease: Reviews and current topics. Vol. Symposium 29. Bethesda, MD: American Fisheries Society.

Franke, M.A. 1997. A grand experiment: The tide turns in the 1950s: Part II. Yellowstone Science 5(1).

Franke, M.A. 1996. A grand experiment: 100 years of fisheries management in Yellowstone: Part I. Yellowstone Science 4(4).

Kerans, B.L. and A.V. Zale. 2002. The ecology of Myxobolus cerebralis. In J.L. Bartholomew and J.C. Wilson, ed., Whirling disease: Reviews and current topics, 145–166. Vol. Symposium 29. Bethesda, MD: American Fisheries Society.

Koel, T.M., D.L. Mahony, K.L. Kinnan, C. Rasmussen, C.J. Hudson, S. Murcia, and B.L. Kerans. 2007. Whirling disease and native cutthroat trout of the Yellowstone Lake ecosystem. Yellowstone Science 15(2).

Koel, T. et al. 2014. Yellowstone Fisheries and Aquatic Sciences Report 2012–2013. National Park Service: Yellowstone National Park.

MacConnell, E. et al. 1997. Susceptibility of grayling, rainbow, and cutthroat trout to whirling disease by natural exposure to Myxobolus cerebralis. Whirling Disease Symposium, Logan, UT.

Murcia, S., B.L. Kerans, E. MacConnell, and T.M. Koel. 2006. Myxobolus cerebralis infection patterns in Yellowstone cutthroat trout after natural exposure. Diseases of Aquatic Organisms 71(3):191–199.

National Exotic Marine and Estuarine Species Information System

National Park Service. 2011. Native Fish Conservation Plan /Environmental Assessment for Yellowstone National Park. Yellowstone Center for Resources.

Varley, J.D. and P. Schullery. 1998. Yellowstone fishes: Ecology, history, and angling in the park. Mechanicsburg, PA: Stackpole Books.

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.

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.

Last updated: May 17, 2023

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Yellowstone National Park, WY 82190-0168



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