Elodea FAQ

No — elodea (Elodea canadensis) and hydrilla (Hydrilla verticillata) are different species. They are in the same plant family (Hydrocharitaceae) and both have whorled leaves, but they are easily separated by three tests: (1) Elodea consistently has exactly 3 leaves per whorl; hydrilla has 4–8. (2) Elodea leaf margins are smooth; hydrilla leaf margins are prominently serrated (toothed). (3) Elodea has no midrib tooth on the leaf underside; hydrilla has a raised tooth on the underside of every leaf midrib. And critically: elodea is a native North American plant with no management concerns in most U.S. states; hydrilla is a federal noxious weed invasive that requires aggressive management. See the full elodea vs. hydrilla guide.

Yes — Elodea canadensis is native throughout most of North America, from British Columbia and Quebec south to the mid-Atlantic states and west to Nebraska and Kansas. It is an ecologically valuable component of native aquatic plant communities across this range. Elodea is invasive in Europe, where it was introduced in the 19th century and became a management problem in British, German, and Scandinavian water bodies, but in its native North American range it is treated as a native plant and is not regulated as invasive. The exception is Alaska, where elodea is non-native and invasive — see the next question.

Elodea is not native to Alaska and was introduced through aquarium releases and floatplane contamination (floatplanes taking off and landing in infested lakes transport elodea fragments on floats and in hull water to new, pristine lakes). In Alaska, where native freshwater ecosystems are sensitive and salmon-rearing lakes and rivers are economically critical, elodea threatens native aquatic plant communities and potentially affects salmon habitat by altering aquatic vegetation structure. The Alaska Department of Fish and Game treats elodea as an invasive species in Alaska and has active eradication programs in affected water bodies. If you observe elodea in an Alaskan lake or river, report it immediately to the Alaska Department of Fish and Game invasive species program.

In most cases, no. Elodea in a natural or semi-natural pond provides fish and invertebrate habitat, oxygen production, and waterfowl food. Removing it simply because it is present is not ecologically justified. If elodea has grown to a density that causes specific problems — obstructing swimming in a swimming pond, blocking a water intake, or covering such a large percentage of a small pond that oxygen depletion is a concern — targeted management may be warranted. Before taking any action, contact your state department of natural resources for guidance. Applying herbicide to native aquatic plants without state authorization may be illegal and is unlikely to produce lasting results without addressing the underlying nutrient conditions driving growth.

Yes — elodea and elodea-like plants are widely sold in aquarium and garden stores under various names including "anacharis," "water weed," "Egeria," and "elodea." The plant sold as "anacharis" is typically either Elodea canadensis or the South American relative Egeria densa (Brazilian waterweed) — not the same species but similar in appearance. Egeria densa is itself invasive in the United States outside its native South American range and has been documented in California, Oregon, Washington, and several other states from aquarium releases. Never release aquarium plants into natural water bodies — this is a major pathway for aquatic invasive plant introduction. The Clean, Drain, Dry principle applies to aquariums too: always dispose of unwanted aquarium plants in the garbage or compost, not in waterways.

Yes — elodea is an efficient aquatic photosynthesizer and produces substantial dissolved oxygen in water, which is why it has been historically popular in the aquarium trade (sold as an "oxygenating plant") and is ecologically valuable in ponds and lakes at moderate densities. In a well-balanced pond with moderate elodea density, the plant contributes meaningfully to daytime oxygen levels and supports fish, invertebrate, and waterfowl communities. However, as with all aquatic plants, very dense elodea growth creates a net oxygen deficit at night — when photosynthesis stops but plant respiration and decomposition continue to consume oxygen. In extremely dense single-species stands, this nighttime oxygen demand can stress fish in small, stagnant ponds. In natural lakes and rivers, elodea at normal densities is a net oxygen producer and ecological benefit. Problems arise only when growth becomes so dense — usually driven by elevated nutrient levels — that nighttime oxygen depletion becomes significant. Maintaining natural plant densities through watershed nutrient management, rather than eliminating elodea entirely, is the appropriate management response in most situations. For guidance on when management is warranted, see elodea control methods.