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The Nonindigenous Occurrences section of the NAS species profiles has a new structure. The section is now dynamically updated from the NAS database to ensure that it contains the most current and accurate information. Occurrences are summarized in Table 1, alphabetically by state, with years of earliest and most recent observations, and the tally and names of drainages where the species was observed. The table contains hyperlinks to collections tables of specimens based on the states, years, and drainages selected. References to specimens that were not obtained through sighting reports and personal communications are found through the hyperlink in the Table 1 caption or through the individual specimens linked in the collections tables.

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Common name: Canadian waterweed

Synonyms and Other Names: Anacharis alsinastrum, Anacharis iowensis, Anacharis canadensis, Anacharis linearis, Anacharis occidentalis, Anacharis planchonii, Anacharis pomeranica, Apalanthe schweinitzii, Elodea brandegeae, Elodea linearis, Elodea brandegeeae, Elodea ioensis, Elodea planchonii, Elodea gigantea, Elodea latifolia, Elodea oblongifolia, Elodea schweinitzii, Hydora canadensis, Philotria angustifolia, Philotria canadensis, Philotria iowensis, Philotria linearis, Philotria planchonii, Serpicula canadensis, Udora canadensis, American duckweed, American waterweed, Broad waterweed, Canada waterweed, Canadian elodea, Canadian pondweed, Common elodea, Ditch weed, Elodea, Oxygen weed, Water thyme, Waterweed, Yankee weed

Taxonomy: available through www.itis.gov

Identification: Elodea canadensis is a perennial, submerged aquatic herb with elongated, leafy shoots between 20-100 cm long, with slender, unbranched roots, and glabrous stems (Spicer and Catling 1988). . The leaves in the middle-to-upper stem branches are 6-17 mm long, 1-5 mm wide, light green, ovate-oblong, ovate lanceolate to linear-lanceolate, and are whorled in groups of three (Spicer and Catling 1988). The flowers have three elliptic sepals, 3.5-5.0 mm long, 2.0-2.5 mm wide and three white petals, 3.5-5.0 mm long, 0.3-0.7 mm wide (Spicer and Catling 1988).

Size: Average height of 1.2 m (3.9 ft), maximum height of 2.5 m (8.2 ft) (Wells et al. 1997).

Native Range: Elodea canadensis is native to much of North America, including Southern Canada, extending to Alabama and California in the United States, especially concentrated around the St Lawrence Valley, the Great Lakes, and the Pacific West Coast (Bowmer et al. 1995; Spicer and Catling 1988; St John 1965).

Alaska	Hawaii	Puerto Rico & Virgin Islands	Guam Saipan

Hydrologic Unit Codes (HUCs) Explained
Interactive maps: Point Distribution Maps

Ecology: Elodea canadensis is a perennial aquatic herb introduced to several river systems across all continents except South America and Antarctica (Kubrak et al. 2012). In North America, E. canadensis is commonly observed in nutrient-rich, neutral to slightly alkaline waters (Spicer and Catling 1988; Holm et al. 1997). The species is typically rooted in mud (Bowmer et al. 1995). It prefers cooler conditions, with an optimum water temperature of 10-25 °C, but has the ability to survive and slowly grow under ice cover (Cook and Urmi-Konig 1985; Bowmer et al. 1995). It is only found in cold water in Australia and has been observed in shallow lakes and streams across Europe and North America (Bowmer et al. 1995; Ersoy and Turan 2019; Josefsson and Andersson 2002). As the plant dies during the fall, it turns black and releases ions, particularly manganese, into the water (Cook and Urmi-Konig 1985).

Seed formation is rare for E. canadensis, instead, the species reproduces vegetatively through dispersal of stem pieces moved by water and waterfowl resulting in rapid growth, especially in soils rich in iron (Spicer and Catling 1988; Cook and Urmi-Konig, 1985; Josefsson and Andersson 2002). Growth in the species occurs immediately after the temperature starts rising and light intensity increases in the spring (Cook and Urmi-Konig 1985; Nichols and Shaw 1986). Its water content can range between 85-95% (Holm et al. 1997). It tends to optimally grow in 3-4 m water depth (Mjelde et al. 2012). In its native range, dense beds of E. canadensis tend to decrease the efficiency of irrigated agriculture (Spicer and Catling 1988). Elodea canadensis provides both cover and food for aquatic invertebrates, in turn, increasing the number of invertebrates and the overall food availability for ducks and fish (Spicer and Catling 1988).

Means of Introduction: In much of its nonnative range,  E. canadensis was introduced through  escape from aquaculture and spreads through fragmentation. It was introduced in Europe after it was privately imported from North America with the purpose of enhancing aquarium culture (St John 1965). It spread quickly from continent to continent and became established across Europe, Africa, Asia, and Oceania (St John 1965).

Status: Elodea canadensis is native to North America and is especially common in the north and eastern regions of the United States as well as the southern region of Canada (Mjelde et al. 2012; Simpson 1986). It is introduced across Europe, Asia, Africa, and Australia (Simpson 1986; Kubrak et al. 2012). It is considered a pest in Europe and a weed in the thermal tropical zone that encompasses India, Thailand, Mauritius, Egypt, Argentina, and Mexico (St John 1965; Holm et al. 1997). In its native range in Canada, E. canadensis is often considered a pest due to its tendency to grow densely and clog waterways and impede watercraft movement (Spicer and Catling 1988).

Impact of Introduction:

Summary of species impacts derived from literature review. Click on an icon to find out more...

Ecological	Economic

Elodea canadensis has been observed altering habitats and changing community structure. In Norway, the spread of E. canadensis resulted in a Najas flexilis (nodding waternymph) dominated community  to become fully dominated by E. canadensis in a 25 year period (Mjelde et al. 2012). Additionally, in Steinsfjord, Norway, the vast spread of E. canadensis displaced every macrophyte across all sediment types (Rørslett et al. 1986). In Poland, the extensive spread of E. canadensis poses a potential threat to various valuable elements of Polish aquatic flora, occupying vegetative land in 40% of the analyzed lakes (Kolada and Kutyla 2016). In three different Swedish lakes, E. canadensis significantly outgrew all native species except Fontinalis antipyretica (Tattersdill et al. 2017).
It is speculated that the first record of E. canadensis in Sapanca Lake in Turkey is a contributing factor in the overall alteration of biodiversity dynamics within the lake (Ersoy and Turan 2019). In Kilpiaistenpohja Bay, Finland, it was found that as the density of E. canadensis increased, the total biomass of the crustacean Daphnia longispina decreased (Kornijów et al. 2004). A study, conducted by the University of Lyon, France found that dense stands of E. canadensis can reduce light penetration, ultimately creating anoxic conditions in the water  (Barrat-Segretain, 2005; Tattersdill et al. 2017).

In Lake Mälaren, Sweden, dense stands of E. canadensis become coated with calcium carbonate, which precipitates in lime-rich waters during photosynthesis periods, raising overall pH (Josefsson and Andersson 2001). Additionally in Central Sweden, low light conditions in water resulting from the cover of dense E. canadensis stands increased phosphate and total organic carbon concentrations (Tattersdill et al. 2017). Elodea canadensis populations in Steinsfjord, Norway stored significant amounts of carbon, nitrogen, potassium, and phosphorous throughout the summer, with nitrogen increasing near the lake floor due to the presence of substantial amounts of ammonium taken from organic decomposition (Rørslett et al. 1986).

Dense stands of E. canadensis obstructed the use of boat ramps in Lake Taupo, New Zealand (Bowmer et. al. 1995). Their dense beds have similarly restricted water traffic and obstructed water-based recreation in Ontario, tBritish Columbia, Southern Quebec, and Alberta (Spicer and Catling 1988).

In addition, E. canadensis has impacted the infrastructure, agriculture, and predation patterns of the environments it’s invaded. Throughout New Zealand, E. canadensis has partially clogged screen intakes in various hydropower stationHoward-Williams 1993).

References: (click for full references)

Barrat-Segretain, M.H. 2005. Competition between invasive and indigenous species: impact of spatial pattern and developmental stage. Plant Ecology 180(2):153-160. https://www.jstor.org/stable/20146803.

Bowmer, K. H., S. W. L. Jacobs, and G. R. Sainty. 1995. Identification, biology, and management of Elodea canadensis, Hydrocharitaceae. Journal of Aquatic Plant Management, 33, 13-19.

Cook, C.D. and K. Urmi-König. 1985. A revision of the genus Elodea (Hydrocharitaceae). Aquatic Botany, 21(2), pp.111-156.

Ersoy, S., and Y.A. Turan. 2019. First report on the cocurrence of invasive macrophyte Elodea canadensis Michx. in Sapanca Lake. European Journal of Biology 78(2):103-107. https://doi.org/10.26650/EurJBiol.2019.0018.

Holm, L., J. Doll, E. Holm, J. Pancho, and J. Herberger. 1997. World Weeds: natural histories and distribution, New York, USA: John Wiley and Sons. Available: https://books.google.la/books?id=i7JjRXH6uq4C&printsec=copyright#v=onepage&q=canadensis&f=false

Howard-Williams, C. 1993. Processes of aquatic weed invasions: the New Zealand example. Journal of Aquatic Plant Management 31:17-23.

Josefsson, M. and B. Andersson. 2001. The environmental consequences of alien species in the Swedish lakes Mälaren, Hjälmaren, Vänern and Vättern. , 30(8), pp.514-521. Ambio: a Journal of the Human Environment 30(8):514-521. https://doi.org/10.1579/0044-7447-30.8.51.

Kolada, A. and S. Kutyla. 2016, Elodea canadensis (Michx.) in Polish lakes: a non-aggressive addition to native flora. Biological Invasions (18) 11: 3251-3264.

Kornijow, R., K. Vakkilainen, J. Horppila, E. Luokkanen, and T. Kairesalo. 2005. Impacts of a submerged plant (Elodea canadensis) on interactions between roach (Rutilus rutilus) and its invertebrate prey communities in a lake littoral zone. Freshwater Biology 50(2):262-276. https://doi.org/10.1111/j.1365-2427.2004.01318.x.

Kubrak, E., J. Kubrak, and P. M. Rowinski. 2013. Application of one-dimensional model to calculate water velocity distributions over elastic elements simulating Canadian waterweed plants (Elodea Canadensis). Acta Geophysica, 61(1), pp.194-210.

Mjelde, M., P. Lombardo, D. Berge, and S. W. Johansen. 2012. Mass invasion of non-native Elodea canadensis Michx. in a large, clear-water, species-rich Norwegian lake–impact on macrophyte biodiversity. In Annales de Limnologie-International Journal of Limnology (Vol. 48, No. 2, pp. 225-240). EDP Sciences.

Nichols S.A., and B. H. Shaw. 1986. Ecological life histories of the three aquatic nuisance plants, Myriophyllum spicatum, Potamogeton crispus and Elodea canadensis. Hydrobiologia, 131, 3–21.

Rørslett, B., D.A.G. Berge, and S.W. Johansen. 1986. Lake enrichment by submersed macrophytes: a Norwegian whole-lake experience with Elodea canadensis. Aquatic Botany 26:325-340.

Simpson D. A. 1986. Taxonomy of Elodea Michx in the British Isles. Watsonia, 16, 1-14.
Spicer, K. W., and P.M. Catling. 1988. The biology of Canadian weeds. 88. Elodea canadensis Michx. Canadian Journal of Plant Science 68:1035-1051.

St. John, H. 1965. Monograph of the genus Elodea, Summary. Rhodora 67(770):155-180.

Tattersdill, K., F. Ecke, A. Frainer, and B.G. McKie. 2017. A head start for an invasive species in a strongly seasonal environment? Growth of Elodea canadensis in boreal lakes. Aquatic Invasions 12(4):487-498. https://doi.org/doi.org/10.3391/ai.2017.12.4.06.

Wells, R. D., M. D. de Winton, and J. S. Clayton. 1997. Successive macrophyte invasions within the submerged flora of Lake Tarawera, central North Island, New Zealand. New Zealand Journal of Marine and Freshwater Research, 31(4), pp.449-459.

Other Resources:
US Fish and Wildlife Service Ecological Risk Screening Summary for Elodea canadensis

Author: Wishah, L., and C.R. Morningstar

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.