The Anglers Guide to Aquatic Invasive Species | By Ecologist Linda Vance

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Many fly anglers became aware of the threat of aquatic invasive species about a decade ago, when felt soled wading boots were implicated in the spread of Didymo and whirling disease, leading to felt bans in several states, and the discontinuation (at least briefly) of felt-soled wading boots by Simms.

Since then, the threats in the U.S. have continued to multiply, affecting fisheries and aquatic ecosystems throughout the country.

See our Acquatic Invasive Species Infographic at the bottom of this article

Overview of Spread | Visible Examples

Those of us who live or fish in the West have also seen a proliferation in the state-mandated watercraft inspection and decontamination stations along main roadways since invasive mussels were found in Lake Mead in 2007[i].

In the Midwest, new reports chronicle the efforts of fish and game agencies to control invasive carp[ii]. First introduced in the Mississippi River drainage to control weeds in canal systems, carp have escaped into the rivers, in some cases entirely eliminating native fish species in local streams.

In the southern US, invasive lionfish threaten both commercial and recreational fisheries, and the very existence of the remaining coral reef ecosystems in the western North Atlantic[iii]

In Alaska, fisheries managers are struggling to eliminate the aquatic weed Elodea spp. This is a fast-growing aquarium species that probably got into the rivers when people dumped the contents of their fish tanks, thinking nothing could survive in Alaska’s cold waters.

Unfortunately, Elodea thrives in slow-moving cold water, impervious to both freezing and drying, growing so rapidly it blocks light and outcompetes all other plant life. As it increases in density, it slows flows, and traps sediments and fine particles that then settle out into spawning gravels, effectively smothering them. Eventually, its own growth causes it to crash, but in death and decomposition, it uses up so much of the available oxygen in the water that other species struggle to survive.[iv]

These high-visibility examples of aquatic invasive species are only a few of the threats we face.

Aquatic Invasive Species (AIS) | Definition

Generally speaking, the term aquatic invasive species (AIS) include all animals, plants and pathogens that have spread outside their native range, and that have a competitive edge over native species, either infecting them with disease, preying on them directly, altering their habitat, or consuming the native species’ food resources.

Deformed Brook Trout

Whirling Disease in Brook Trout

Intentionally Introduced

Sometimes, invasive species have been intentionally introduced by anglers, as in the case of Northern Pike in California[v], or walleye in Idaho’s Lake Pend Oreille, where they preyed on and outcompeted native trout and salmon.[vi] In some cases, no one has identified the origin of an invasion. In Yellowstone National Park, for example, lake trout “appeared” in Lake Yellowstone in 1994. By 2005, the population was close to a million fish, with catastrophic impacts to the park ecosystem.

Spawning cutthroat numbers fell from 50,000 in the 1980s to less than 500, and soon, the eagles, osprey and bears that depended on spring spawners for food began spreading out in search of other nutrient sources, like swans and baby mammals. While park biologists have recently started to gain the upper hand in controlling lake trout, the effort is costing the park over $2 million each year.[vii]

Invasive Plant Species

Invasive plant species can also impact trout populations. In lake and pond ecosystems, introduced plants like flowering rush, non-native common reed, giant salvinia and water hyacinth quickly colonize open water.

While this can be beneficial to the young of some fish species, it reduces spawning opportunities for others, and provides cover for lie-in-wait predators, gradually altering fish population composition. And in some cases, water hyacinth and giant salvinia can create such dense mats that oxygen exchange is limited, affecting fish growth and even survival.[viii]

eichhornia crassipes
Water Hyacinth

Salvinia Molesta
Giant Salvinia
The aquatic fern, Salvinia molesta, photographed in Hawai‘i by Eric Guinther

How much are anglers implicated in the spread of invasives?


So how much are anglers implicated in the spread of invasives? Clearly, the “bucket biologists” who intentionally introduce non-native fish species into lakes and rivers are among the worst offenders, as are those bait fishers who know better, but who dump their remaining live bait into waterways at the end of the day.[ix]

Any boater who plots their route to or from a favorite spot to avoid watercraft inspection has a serious case of indifference to the problem. But those of us who simply switched from felt to rubber soles and called it good are also part of the problem.

Who among us hasn’t put on damp waders in the morning, or visited a couple of different streams in a single day, or travelled between watersheds on a weekend angling trip? And how many of us pay attention to the less-obvious ways we can introduce invasives, like carrying seeds or other plant materials on the Velcro closures on sandals or vest patches?

What Can Anglers Do To Help Stop the Spread?

If we are genuinely concerned about the health of aquatic ecosystems and fisheries, there are a number of actions we can all take

1. Know the Enemy.

First, know the enemy. If you don’t know what Didymo looks like, get online and find out. Know which streams and rivers in your home watershed have reported whirling disease, and make sure to do your homework before you venture out (and return from) a new place.

Photographed in New Zealand by Thorney¿? 

Find out what the threats are in your home state, and the states that border you.

The United States Geological Survey maintains an excellent website for Nonindigenous Aquatic Species at, where you can search for invasive species information by state, drainage, or species, and view both presence and threat maps. I just touched on invasive invertebrates in this article; the USGS site has listings for 70 invasive clam and mussel species.

2. Take time to take care

Second, take time to take care. Regardless of what kind of soles you use, regard your wading footgear as potential sources of contamination. Cleaning your boots, waders, sandals, net, and other gear is a pain, especially in the middle of the day when you’ve decided to head for your next favorite stream. But do it anyway.


I often carry two sets of wading gear when I think I might switch streams mid-day: boots and chest waders for the cool morning, hip waders or nylon pants with sandals for the afternoon if temperatures permit. If that is out of reach for you, invest in a stiff brush, a heavy plastic container, a plastic tub and a gallon of disinfectant so you can move from one stream to another without risking the spread of invasives..

While chlorine bleach solutions will work against many aquatic invasive species, bleach is also hard on your gear.

Instead, both for work and recreation, I follow the recommendations of multiple state and federal agencies and use a quaternary ammonia compound.[x] I mix Super HDQ neutral (available from Amazon), at a ratio of 6 oz to a gallon of water, and keep it in a dedicated 7 gallon water jug (labelled TOXIC with a sharpie). .

After thoroughly brushing my boots and wader seams, I stick them in the plastic tub, pour the disinfectant solution over them, and sort my flies for ten minutes. A good brushing that removes mud and debris will also keep the solution clean enough to pour back into the container and use again.


If you don’t travel between streams on the same day, you can disinfect at home. Or, if you are looking for a less labor-intense solution, try freezing. While there are some reports that mussels can withstand freezing, brushing your waders and boots and tossing them into a chest freezer overnight should kill most organisms.

Hot water is another option: after brushing, soak waders and boots in water hotter than 115 F for 15 minutes. [xi] The hottest tap water in most homes and motels will exceed that temperature. Although I don’t know of any studies to support it, there is anecdotal support for the idea that running your boots through a clothes dryer on hot for long enough to completely dry them will also kill invaders.

3. Watercraft

Third, when you use a watercraft –whether it’s a boat, a paddleboard, a kayak or a float tube- follow the Inspect, Drain, Clean and Dry protocol.

Pick all visible debris off and leave out to dessicate. If you have a hard sided watercraft, run your hand across the hull; if it feels like sandpaper, you may have picked up mussels.

Didymo Sign

Didymo Sign
Photographed in New Zealand by Thorney¿? 

Drain any chamber or well that may contain water (including the bow and stern of your sit-in kayak.

Clean the watercraft with hot water (140 degrees F), pressure wash it, or, if you live in a state with disinfecting stations, run it through their wash. Leave everything to dry thoroughly before reusing.

zebra mussel
Zebra Mussel

new zealand mud snail
New Zealand Mud Snail
Photographed by Michal Maňas – Maňas M. (2014).

4. Get involved

Fourth, get involved. The University of Georgia has created its WildSpotter App for smartphones so that you can report the invasives you encounter. Depending on your state, there may be similar, state-specific apps you can use.

Check with your local watershed group or Trout Unlimited to find invasive species removal events. Many of these events have been on hold during the pandemic, leaving aquatic invasive plants plenty of opportunity to expand; as the country reopens, expect more volunteer cleanup events to expand as well.

5. Be bold

Finally, be bold. Challenge your bait-fishing friends and family to find out exactly what species they’re buying when they pick up live bait.

Pay attention to your kids’ school science projects: are they raising guppies in bowls filled with Elodea?

Look for water garden displays at your local garden center and find out exactly what they’re selling; you’ll be surprised how heavily “fast growing water hyacinth” is promoted. Make a stink about it. Question what you bring into your own garden, and find out what might happen if it escapes to nearby riparian areas.

And talk to the anglers you meet. The pandemic has dramatically increased the number of new fly anglers; according to a Redington marketing manager I spoke with, the fly fishing industry hasn’t seen a run on gear this large since A River Runs Through It was released, and, he said, this new wave of interest far surpasses even that one.

This means that we have more people with less knowledge of invasive species moving around in our favorite streams. Instead of just grumbling about how they’re taking over, spend time talking to them to make sure overcrowding isn’t the only negative impact they bring.

Guide to Invasive Species | Infographic

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Aquatic invasive species are a miserable reality, one we would all prefer did not exist. In the long run, perhaps the best we can do is slow their spread, or work on reducing their impacts in our local streams and lakes. It will take more than the quiet, passive action of changing our boots and disinfecting our gear; we will need to look up from that perfect pocket water where there just has to be a trout, and pay attention to the entire watershed, and the other anglers fishing it.

But if we believe what we say, that we are committed to preserving the waters and fish we love for future anglers to enjoy, we can take the small and large steps required to make that future a reality.

From Anchor Fly

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About the author:

Linda Vance has a Ph.D in Aquatic Ecology from the University of California at Davis. She is Associate Director of the Center for the Rocky Mountain West at the University of Montana, where she leads the Ecological Mapping, Monitoring and Assessment Group (EMMA).


During the summer months, she supervises several dozen EMMA staff and seasonal technicians who work across the Western US, surveying stream health and evaluating fish habitat on public lands. From the very first day of training through the last day of the season, staff and technicians are expected to follow chemical disinfectant protocols, no matter how dirty and tired they are, or how hot and smoky their surroundings.


[i] Press Release, “Invasive mussel update from Lake Mead National Recreation Area.” Available at:
[ii] “Carp Advance: Real and potential impacts of invasive fish throughout the Midwest,” Great Lakes Now.
Available at:
[iii] NOAA Aquatic Invasive Species Factsheet: Invasive Lionfish. Available at:
[iv] Larson, A. and T. Simmons. 2020. “Elodea: Alaska’s First Invasive Aquatic Plant Continues to March
Across the State.” Alaska Park Science 19(1). Below the Surface: Fish and Our Changing Underwater
World. Available at:
[v] California Department of Fish and Wildlife. California’s Invaders: Northern Pike. Available at
[vi] Idaho Department of Fish and Game. “Lake Pend Oreille Walleye Update.” July 3, 2018. Available at:
[vii] USGS Northern Rocky Mountain Science Center. “FAQ on Invasive Lake Trout in Yellowstone Lake.”
Available at:
[viii] Aquatic invasive plants are plentiful across the country. For a comprehensive list and accompanying
fact sheets, visit the Center for Invasive Species and Ecosystem Health at
[ix] Snyder, M.R., C.A. Stepien, N.T. Marshall, H. B. Scheppler, C.L. Black, and K.P. Czajkowski. 2020.
“Detecting aquatic invasive species in bait and pond stores with targeted environmental (e)DNA high-throughput sequencing metabarcode assays: Angler, retailer, and manager implications.” Biological Conservation 245, 108430. Available at
[x] Some people are sensitive to Super HDQ Neutral, and will develop a rash. If you wear your waders (or neoprene socks) over bare skin, test it out before soaking everything you own, or rinse again after soaking. The disinfectant protocols from the Colorado Department of Wildlife list a number of alternative products that also work well:
[xi] Anderson, L.G., A.M. Dunn, and P.G. Rosewarne. 2015. “Invaders in hot water: a simple decontamination method to prevent the accidental spread of aquatic invasive non-native species”. Biological Invasions 17, 2287–2297. Available at:
Photo of author
Linda Vance has a Ph.D in Aquatic Ecology from the University of California at Davis. She is Associate Director of the Center for the Rocky Mountain West at the University of Montana, where she leads the Ecological Mapping, Monitoring and Assessment Group (EMMA).

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