Frequently Asked Questions


What is Elodea, and why is it a threat?

Where has Elodea been found, and how do we know it is not native to Alaska?

What is being done to control Elodea or prevent its spread?

What is Elodea, and why is it a threat?

Q: What is Elodea?

A: Elodea is a rooted, submerged aquatic plant. It grows in slow-moving or still clear waters, and is invasive in much of Europe, Asia and Australia. Elodea can spread by small broken fragments. It is commonly used as an aquarium plant.

Q: What problems may Elodea cause in Interior Alaska?

A: In other places, Elodea has made large-scale changes in freshwater ecosystems.  The dense vegetation can change water quality, increase sedimentation, degrade salmon spawning habitat, displace native vegetation and act as a physical barrier to fishing and boat travel. In Chena Slough and Totchaket Slough, we already see areas nearly impassible due to dense Elodea growth. These rivers are upstream of many other natural water bodies Elodea could potentially infest.

Where has Elodea been found, and how do we know it is not native to Alaska?

Q: Where has Elodea been found in Alaska?

In Interior Alaska, Elodea was discovered in 2009/2010 in Chena Slough. Surveys the following two years additionally found infestations in Chena Lake, near North Pole, and in small patches in the Chena River. In the fall of 2015, Elodea was found in Totchaket Slough, a tributary of the Tanana river north of Nenana.

Elsewhere in the state, it has been found in three float plane lakes in Kenai, three lakes in the Anchorage bowl, and several lakes in Cordova, Alaska.

Q: I read on Wikipedia that Elodea is native to most of North America. Why are you saying it is an invasive species here? Couldn’t it be extending its range, maybe caused by the warming climate?

A: Prior to 2009, Elodea was found only once in Alaska: in Eyak Lake near Cordova about thirty years ago. Currently, it is only found in waters adjacent to urban areas. Extensive botanical surveys in remote areas of Alaska have failed to discover Elodea. Because of these pieces of information, botanists agree that it is likely a non-native species. In addition, the ability to grow aggressively in Chena Slough demonstrates the same invasive tendencies that Elodea has shown repeatedly in other places that it has been introduced (e.g. Europe, Asia, and Australia).

For more detail on this question, please read this letter on Elodea's non-native status.

What is being done to control Elodea or prevent its spread?

Q: How is Elodea being managed in interior Alaska?

The integrated pest management approach proposed consists of herbicide (fluridone) treatment in Chena Slough, Totchaket Slough and Chena Lake, and continued manual removal for the patches of Elodea in the Chena River.

Q: Why is herbicide treatment being considered, instead of solely mechanical treatment?

For the past 3 summers, the Fairbanks Soil and Water Conservation District in conjunction with Test the Waters dive shop have been testing manual removal of Elodea in Chena Slough. Using a suction dredge in deep waters and rakes in shallow areas, whole plants were uprooted, loaded onto self-bailing rafts, bagged and removed from the site. In 2013, volunteers worked for 280 hours and removed 0.59 acres of Elodea. In 2014, volunteers worked for 250 hours and removed 1.34 acres of Elodea. In 2014 it was found that Elodea had regrown in 4 patches. Due to the amount of labor required, the likelihood of regrowth and the potential for fragmentation (and spreading Elodea elsewhere), manual control is not able to eradicate Elodea.

The Elodea Steering Committee is now pursuing the use of herbicides to remove Elodea from Chena Slough, Totchaket Slough and Chena Lake. The minor infestations in Chena River will continue to be removed via suction dredging. Herbicide treatment appears to be successful in Kenai and Anchorage area lakes in eradicating Elodea.

Q: What is fluridone?

Fluridone is a slow-acting systemic herbicide used to control Elodea, hydrilla, Eurasian watermilfoil and other underwater plants. Like other systemic herbicides, fluridone is absorbed from water by plant shoots and from the hydrosoil by the roots of aquatic plants. It inhibits the formation of carotene, a plant pigment, causing the rapid degradation of chlorophyll by sunlight, which then prevents the formation of carbohydrates necessary to sustain the plant.

Q: Is fluridone treatment safe for humans?

Yes. As fluridone interferes with photosynthesis, the risks to human health are minimal. Below the EPA limits of 150 parts per billion (ppb), water treated with fluridone is safe to swim in and drink. To observe any toxic effects, a 150 lb. adult would have to drink over 1,000 gallons of water containing 150 ppb fluridone every single day for a significant portion of their lifetime. Concentrations of fluridone in Chena Slough, Totchaket Slough and Chena Lake will be maintained at the low concentration of 4-8 ppb, and, generally, drinking surface waters is not recommended.

Fluridone binds to soil, and does not interact with groundwater. It degrades from sunlight and microbial activity.

Q: What impact will treatment have on fish and wildlife?

Fluridone applied at the approved concentration rate has not been found to be toxic to waterfowl and wildlife. Laboratory animals (mice, rats, dogs) fed with fluridone in their diets showed little signs of toxicity even when fed levels which far exceed potential human exposure from use of fluridone. Fluridone is not considered to be a carcinogen or mutagen and is not associated with reproductive or developmental effects in test animals (WADOH, 2000).

No adverse effects were observed on crayfish, bass, bluegill, catfish, long-neck soft-shell turtles, frogs, water snakes, and waterfowl from the use of 100 to 1000 ppb of fluridone during field experiments (Arnold 1979, McCowen et al, 1979). Zooplankton were reduced slightly when 1000 ppb was applied, a substantially higher dosage than will be used in the Fairbanks area treatment, but populations quickly recovered. Target concentrations for interior Alaska waters are 4-8 ppb.

Q: What will happen to native plants in areas treated with fluridone?

Fluridone will also interfere with photosynthesis in native plants. However, Elodea is unusually susceptible to fluridone, and at these low treatment concentrations, it is expected to be the only plant eradicated. The native plant community should recover completely within a year after treatment ceases.

Q: Are there any downsides to fluridone treatment?

Water quality is expected to degrade slightly during treatment, as decaying plants use up dissolved oxygen. Dissolved oxygen should recover after treatment ends.

The EPA recommends plants should not be irrigated with water containing more than 10 pbb fluridone.

Q: What can I do to prevent the spread of Elodea?

A: Familiarize yourself with what Elodea looks like, and report any possible infestations. When boating or recreating in water, completely clean any boats, trailers, etc, and allow them to dry before entering another water body.

If you'd like to stay informed about Elodea in the Fairbanks area, please subscribe to our mailing list:

Elodea mailing list


*12/3/2010, written by T. Wurtz, N. Lisuzzo, and A. Larsen

*12/9/2015, edited by C. Miller

Bureau of Land Management - Fairbanks District Office Alaska Department of Fish and Game Department of Transportation and Public Facilities – Northern Region USKH Inc. Fairbanks North Star Borough - Parks & Recreation National Park Service