When Is Elodea Management Warranted?
The management philosophy for elodea differs fundamentally from that for invasive species like hydrilla and Eurasian watermilfoil. In most of the continental United States, elodea is a native plant with ecological value. Management is only warranted when elodea has reached densities that cause meaningful harm — not simply because it is present and visible. In the continental U.S., management of nuisance native elodea follows the same general philosophy as coontail management: target density reduction, not elimination, and preserve the ecological functions the plant provides at lower density.
The major exception is Alaska, where elodea is non-native and invasive. In Alaska, elodea management goals are eradication or long-term suppression to protect native fisheries — an entirely different management objective that uses more aggressive management approaches. This guide covers both continental U.S. nuisance management and Alaska invasive management.
Permits Required: Any aquatic herbicide application — even for a native plant — requires permits from your state's department of natural resources or environmental protection agency. Contact your state agency before beginning any management program.
Continental U.S.: Nuisance Native Plant Management
When Management Is Justified
Management of native elodea in continental U.S. water bodies is justified when: dense elodea growth is causing measurable harm to recreation (navigation obstruction, swimming impairment) or threatening oxygen levels in small ponds; elodea is growing at densities where it has displaced all other native plant diversity (a symptom of eutrophication that needs to be addressed at the nutrient level); or growth is occurring in artificial water bodies (canals, stormwater basins) where natural plant communities are not a management goal. In natural lakes with diverse native plant communities, elodea at any density is generally considered part of the native plant community and does not warrant control.
Nutrient Reduction First
Like coontail, dense native elodea growth is almost always driven by eutrophication. Addressing nutrient inputs from the watershed is the most important long-term management action. Without nutrient reduction, any elodea control treatment will be followed by rapid regrowth.
Mechanical Harvesting
Mechanical harvesting is the most ecologically appropriate management tool for nuisance native elodea — it reduces biomass without chemical inputs, can be targeted to specific high-density areas, and preserves native plant recovery. Aquatic harvesters cut and remove biomass from the water. Harvested material must be fully removed from the water body and composted on land.
Herbicide Treatment
Herbicide treatment is occasionally warranted for nuisance native elodea in situations where mechanical treatment is impractical. Registered aquatic herbicides including endothall and diquat (contact), and fluridone (systemic at whole-pond concentrations) can reduce elodea density. Treatment of native plants with herbicide should always be discussed with your state DNR before proceeding.
Alaska: Invasive Elodea Management
In Alaska, elodea is treated as an invasive species and the management goal is eradication or long-term suppression. The Alaska Department of Fish and Game and the Alaska Department of Environmental Conservation coordinate elodea management in infested water bodies. Herbicide eradication programs using aquatic herbicides (primarily fluridone) have been conducted in several Alaska lakes with good early-season detection results. Prevention through floatplane decontamination (decontaminating float plane floats that have been in infested water before flying to other lakes) and early detection programs are critical components of Alaska's elodea management strategy. Contact the Alaska Department of Fish and Game invasive species program for current management guidance if elodea is suspected in an Alaskan water body.
Monitoring and Long-Term Management
Whether managing invasive elodea in Alaska or monitoring native elodea density in the continental U.S., consistent annual aquatic plant surveys provide the baseline data needed for sound management decisions. Early detection of new elodea establishment — particularly in Alaska water bodies where it has not been previously documented — allows rapid response before populations grow to levels requiring costly eradication programs. In the continental U.S., annual surveys in lakes with a history of nuisance native elodea density allow managers to track whether density is declining (treatment working), stable, or increasing (additional management warranted). Monitoring should include transect-based surveys in late summer when biomass is at its seasonal peak, with GPS-referenced mapping of plant coverage. Survey results should be submitted to your state's aquatic plant monitoring database where one exists. For identification confirmation, see the elodea identification guide and the elodea vs. hydrilla comparison.
References
- Alaska Department of Fish and Game. Elodea in Alaska — Management Overview. adfg.alaska.gov
- Nichols, S.A. (1991). The interaction between biology and management of aquatic macrophytes. Aquatic Botany 41:225–252.