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Arizona's Top 10 Most Unwanted Species

Giant Salvinia

This species has already invaded the Colorado River near Yuma and efforts are underway to try and eradicate it. This species is a free-floating aquatic fern from southeastern Brazil. It is an aggressive invader that is tough to eradicate. In parts of Texas and Hawaii, giant salvinia has formed mats so extensive that migratory birds can no longer nest or forage in their usual areas. In Texas, anglers find it difficult to cast into water covered with thick mats of giant salvinia.

American Bullfrog

Bullfrogs are not native to Arizona. These voracious amphibians eat native species, such as native fish and native frogs, including a long list of species on the endangered species list. Bullfrogs are native to the eastern United States. They are thriving in Arizona, to the detriment of a host of native species. Bullfrogs were originally introduced because of their tasty legs. There is a year-round season on them in Arizona. Please harvest and eat all of them you can.


Arizona is the only state in the continental United States where crayfish are not native. Because crayfish are a non-native species, they are not a natural part of Arizona's aquatic ecosystem. In some areas, crayfish are negatively impacting sport-fishing opportunities - especially some high country trout streams. Please catch and keep all the crayfish you can (a fishing license is required for anyone 14 year of age and older). However, there are regulations prohibiting the transport of live crayfish from one water to another in the state.

Zebra Mussels

Zebra mussels and a related species, the Quagga mussel, are small, fingernail-sized mussels native to the Caspian Sea region of Asia. They were discovered in Lake St. Clair near Detroit in 1988.

Twice during the summer of 2004, Zebra mussels were found on the hulls of boats from out of state. Fortunately, those boats were prevented from entering Arizona waters until they were decontaminated.

Tolerant of a wide range of environmental conditions, zebra mussels have now spread to parts of all the Great Lakes, the Mississippi River, and are showing up in inland lakes. Zebra mussels clog water-intake systems of power plants and water treatment facilities, as well as irrigation systems, and the cooling systems of boat engines.

Zebra mussels have severely reduced, and may eliminate native mussel species. Female zebra mussels can produce as many as 1 million eggs per year. They filter the zooplankton, which is a good source for forage fish and for young sport fish.

New Zealand Mudsnail

This tiny creature has already been found in the Colorado River below Glen Canyon Dam to about the Diamond Creek area of the Grand Canyon. The mudsnail was probably introduced to North American in shipments of trout eggs from New Zealand. The snail was discovered in Idaho's Snake River in 1987, where it now exceeds 100,000 snails per square meter along some reaches of river.

These invasive snails have an extraordinary survival mechanism: they close a trap door in their shells when they are eaten by fish and birds, which allows them to pass through undigested, depriving the birds and fish of any nutrition. In the Madison River in Yellowstone National Park, the New Zealand mudsnail now outnumbers all native mollusks.

Northern Snakehead

Snakeheads are voracious predators and are exceptionally successful in competing with other fish for food and habitat. The northern snakeheads have the ability to reproduce up to five times a year and are aggressive at protecting their young. The northern snakehead also has a wide temperature tolerance.

If snakeheads were to become established in Arizona, they could severely impact existing sportfish populations. Although they are not found in Arizona, snakeheads have been found in California, Florida, Maryland, Massachusetts, North Carolina, Pennsylvania and possibly other states.


Hydrilla has been found in isolated locations in Arizona, but has been controlled or eradicated. Hydrilla seriously effect water use and flow. Hydrilla will block sunlight penetration, which ultimately impacts boating, fishing and swimming. Water quality becomes degraded due to oxygen depletion.

Hydrilla spreads through vegetative fragments. Transportation on boating equipment plays the largest role in introducing hydrilla fragments to new bodies of water.

Golden Algae

Golden algae were discovered in Arizona in 2005. They can produce a powerful toxin that enters the blood stream of fish across the gill membrane and cause asphyxiation. All fish species can be affected. The number of fish killed depends on how long the bloom remains active and toxin present.

Golden algae was first identified in Israel, then showed up in Texas in 1985. Since then, golden algae has caused fish kills in Oklahoma, Colorado, New Mexico, North Carolina, Nebraska, Kansas, Iowa, Arizona and possibly other states.

Asian Carp

Silver and bighead carp have not yet been found in Arizona. There is potential for Asian carp to be inadvertently mixed in legally sold minnows at bait shops. This is a prime example of why anglers should never dump live bait into waters and why they should dispose of bait properly. Silver and bighead carp damage habitats and consume vast amounts of food. In addition, Silver carp leap out of the water when startled by noise and vibrations caused by boats, motors and even paddling. Boaters are occasionally injured or knocked out of their boats.

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Check out the Latest News about the Stop Aquatic Hitchhiker Campaign and the aquatic hitchhiker problem.

Common Hitchhikers

Zebra Mussels
Whirling Disease
Spiny Water Fleas
Round Gobies
Water Hyacinth

Video Clips
Asian Carp in the Upper Mississippi River
(Real Video format)

Round Goby
(Quicktime Format)
New Audio Messages for Traveler Information Systems
Zebra Mussel (mp3)
Zebra Mussel #2 (mp3)