Elodea nuttallii

Canadian waterweed (Elodea canadensis) 

Nuttall’s waterweed (Elodea nuttallii) 

Photos © Armin Jagel, www.botanik-bochum.de 

Common name(s) 

in English 

Elodea canadensis: Canadian waterweed. Common waterweed. 

American waterweed. American elodea. Canadian pondweed. Water 

thyme. Ditch moss. Broad waterweed. Anacharis. 

Elodea nuttallii: Nuttall’s waterweed. Nuttall’s pondweed. Western 

waterweed. Free flowered/free-flowering waterweed. Nuttall’s water 

thyme. 

… and in other languages 

Canadian waterweed: Danish: Vandpest. Almindelig vandpest. 

Dutch: Brede Waterpest. Estonian: Kanada vesikatk. Kanada vesihain. 

Finnish: Vesirutto. Kanadanvesirutto. French: Elodée du Canada. Peste 

d’eau. German: Kanadische Wasserpest. Latvian: Elodeja. 

Lithuanian: Kanadine elodeja. Norwegian: Vasspest. Polish: Moczarka 

kanadyjska. Swedish: Vattenpest. Vanlig vattenpest. 

Nuttall’s waterweed: Danish: Smalbladet vandpest. Dutch: Smalle 

Waterpest. German: Schmalblättrige Wasserpest. Nuttalls Wasserpest. 

Swedish: Smal vattenpest. 

Scientific name 

Organism group 

Canadian waterweed: Elodea Canadensis 

Nuttall’s waterweed: Elodea nuttallii 

Vascular plants. Frogbit family (Hydrocharitaceae).

Size and appearance 

Canadian waterweed: Has long, trailing stems that can grow to a 

couple of metres in length. The leaves, which are 6–15 mm long and 

1.5–4 mm wide, are arranged in whorls along the stem. The plant has 

white, thread-like roots. The white, single-sex flowers appear from 

July to September. 

Nuttall’s waterweed: Like Canadian waterweed, has trailing, metrelong 

stems. As in that species, the leaves are arranged in whorls, but 

here they are slightly shorter (6–13 mm) and appreciably narrower 

(no more than 1.5 mm), and they may be a somewhat paler green. In 

general, plants of this species are somewhat smaller and more 

“delicate” than Canadian waterweed. 

Both species: Male and female flowers are produced on different 

plants. So far, only female plants of the two species have been found 

in Europe. The species reproduce vegetatively by means of loose 

fragments and stem tips that disperse by water or are carried to new 

sites by birds or humans. Even tiny fragments can develop into new 

plants. 

May be confused with 

The two species may be confused with each other, but, as indicated 

above, Canadian waterweed (Elodea canadensis) has broader leaves 

than Nuttall’s (E. nuttallii). In Canadian waterweed, the leaves of the 

stem tip are broad and tongue-like, rather than narrow and strongly 

recurved. Nuttall’s waterweed has a more freely branched stem. 

Another difference between the species is that in Nuttall’s waterweed 

the male flowers (which admittedly are rarely produced) break off and 

float to the surface. Nuttall’s waterweed is still considerably rarer than 

Canadian waterweed, but seems to be spreading ever more widely in 

Europe and may even, in places, have the potential to outcompete its 

relative. 

A closely related species, Brazilian elodea or Brazilian waterweed 

(Egeria densa), is often sold for use in aquaria. 

Geographical origin 

Canadian waterweed: North America: Canada. 

Nuttall’s waterweed: North America (named after Thomas Nuttall, who 

studied the flora of the American West in the early 19th century). 

First observed in 

Swedish waters 

Occurrence in 

Swedish waters 

Canadian waterweed: 1871, in ponds in the Uppsala area. 

Nuttall’s waterweed: 1991, at Ängby near Stockholm. 

Canadian and Nuttall’s waterweed are freshwater plants, and do not 

occur in salt water or in brackish water too strongly affected by salt 

water (see below regarding habitats). Canadian waterweed is to be 

found, however, in Swedish and Finnish coastal waters of the Gulf of 

Bothnia, for instance in confined inlets in areas where marked 

postglacial crustal uplift is occurring. 

In fresh waters, Canadian waterweed is found widely across Sweden, 

from Skåne in the south to Dalarna in the north, with some 

occurrences even further north. Less is known about how common 

Nuttall’s waterweed is, but the species has been found in various 

freshwater bodies in Skåne, Västergötland and Norrbotten. In Lake 

Mälaren, this species is more abundant than Canadian waterweed. 

Occurrence in other 

areas (coastal or 

inland waters) 

Canadian waterweed: Was introduced to Europe from North America 

around 1840. It is reported to have been discovered for the first time 

in Europe in 1836, in a pond in Ireland, and six years later finds were 

made in Britain (Scotland). The first find in Germany was in 1859, in

the vicinity of Berlin. Today the species occurs throughout Germany, 

but is beginning to be supplanted by its relative Nuttall’s waterweed. 

Canadian waterweed is now also to be found throughout Poland. The 

species was first recorded in Denmark in 1870 (and is now established 

and common there), in Sweden in 1871 (now established and 

common), in Finland in the 1870s (now established and common), but 

not until 1925 in Norway. It was discovered in Estonia in 1905 (now 

established and common), in Latvia in 1872 (now established and 

common), in Lithuania in 1884 (now established and common), and in 

European areas of Russia in 1870 (now established and common). 

Canadian waterweed has also spread to countries in Asia, to Australia 

and New Zealand, and from Europe on into North Africa. 

Nuttall’s waterweed: Was probably introduced into Europe from North 

America in the 20th century. When the species was first discovered in 

Britain in 1914, however, it was identified as Hydrilla verticillata, and a 

definite identification of Elodea nuttallii was not made until 1974. From 

the continent of Europe, finds were reported from Belgium in 1939 

(with a definite identification in 1955) and the Netherlands in 1941. In 

Germany the species was discovered in a botanical garden in 1953, 

and has since spread across the country. There are also reports of 

finds in Denmark (1974). It is not unlikely that additional finds have 

been made, but that they have been mistaken for Canadian 

waterweed. Nuttall’s waterweed now appears to be becoming 

increasingly widespread, even to the extent of outcompeting Canadian 

waterweed. 

Probable means 

of introduction 

Habitat(s) in which 

species occurs 

Canadian waterweed may have been used in aquaria, which were then 

emptied into rivers and lakes. In addition, the species may have 

accompanied other plants or timber imported into Europe. Further 

dispersal to neighbouring countries, or within countries, can also be 

brought about by birds. Movements of recreational craft between 

water bodies are another means by which the species can spread. 

Canadian and Nuttall’s waterweed are freshwater species, but also 

occur in brackish-water areas significantly affected by fresh water 

(confined inlets, estuaries). In general, though, Canadian waterweed 

and, to an increasing extent, Nuttall’s waterweed are chiefly to be 

found in lakes, ponds, slow-moving rivers and wetlands. 

Both species are submerged plants. They prefer calcareous, nutrientrich 

waters (pH 6.5–10) and sediments, and grow best on firm 

substrates with a high mineral content. In eutrophicated waters they 

have a competitive advantage over other aquatic plants. They also 

contribute to internal nutrient cycling in water bodies, as they take up 

nutrients from sediments. These species are tolerant of shade and are 

therefore able to survive even in turbid waters. Although they are 

freshwater plants, they can cope with salinities of up to 2.5 psu. The 

optimum water temperature range is 10–25°C, but both species can 

withstand quite cold water. Under a layer of closed, snow-covered ice, 

plants can survive even in water at a temperature of just 1–4°C. The 

two species tend to grow in relatively shallow water, preferably no 

deeper than about 3 m, but Canadian waterweed has been found down 

to depths of 16 m. Nuttall’s waterweed seems to be able to grow in 

deeper water than Canadian. 

Ecological effects Both these Elodea species form dense stands – like thick carpets – 

that reach all the way to the surface of the water. This compact mass 

of plant material prevents penetration of sunlight, changing conditions 

for other plants. Animal life, too, is affected by the dense, spreading 

stands. In addition, the nutrient status of the water can be altered if 

large quantities of biomass from the species are broken down, 

exacerbating eutrophication. As they grow, Canadian and Nuttall’s

waterweed can displace other plant species. 

Other effects 

Additional information 

Dense canopies of Canadian and Nuttall’s waterweed cause significant 

problems for boat traffic and fisheries. A large abundance of these 

species also makes waters unsuitable for bathing and other 

recreational uses. 

Elodea canadensis is also known by several synonyms: 

• Anacharis canadensis 

• Anacharis canadensis var. planchonii 

• Elodea brandegae 

• Elodea ioensis 

• Elodea linearis 

• Elodea planchonii 

• Helodea canadensis 

• Philotria canadensis 

• Philotria linearis 

For Elodea nuttallii, too, there are several synonyms: 

• Anacharis occidentalis 

• Anacharis nuttallii 

• Elodea columbiana 

• Elodea minor 

• Elodea occidentalis 

• Philotria angustifolia 

• Philotria minor 

• Philotria nuttallii 

• Philotria occidentalis 

• Udora verticillata var. minor 

FIND OUT MORE: Canadian waterweed (Elodea canadensis) 

• Swedish Museum of Natural History: (Virtual flora): Vattenpest (Elodea canadensis) 

In Swedish only 

http://linnaeus.nrm.se/flora/mono/hydrocharita/elode/elodcan.html 

• North European and Baltic Network on Invasive Alien Species: Elodea canadensis 

http://www.nobanis.org/speciesInfo.asptaxaID=822 

• Wikipedia: Vattenpest (Elodea canadensis) 

http://sv.wikipedia.org/wiki/Vattenpest 

• BioPix: Vattenpest (Elodea canadensis) 

http://www.biopix.dk/Species.aspLanguage=sv&Searchtext=Elodea%20canadensis&Category=Planter 

• Baltic Sea Alien Species Database: Elodea canadensis 

http://www.ku.lt/nemo/directory_details.phpsp_name=Elodea+canadensis 

• Alien species in Poland: Elodea canadensis 

http://www.iop.krakow.pl/ias/species.asp83 

• European Nature Information System Database (EUNIS): Elodea canadensis 

http://eunis.eea.europa.eu/species-factsheet.jspidSpecies=186340&idSpeciesLink=186340 

• Aquatische Neopyhten in Nordrhein-Westfalen: Elodea canadensis 

http://www.aquatischeneophyten.de/Webseiten%20NEU/Pflanzenseiten%20neu/Elodea%20canadensis.htm 

• Botanischer Garten, Ruhr-Universität Bochum: Elodea canadensis 

http://www.ruhr-uni-bochum.de/boga/html/Elodea_canadensis_Foto2.html 

• 82 kB: DAEC, Bureau de protection de la nature et du paysage du canton de Fribourg: 

Elodée du Canada. 

http://www.fr.ch/pna/neophytes/fiches/elodee.pdf 

• Ulster Museum Sciences Division: Flora of Northern Ireland: Elodea canadensis 

http://www.habitas.org.uk/flora/species.aspitem=2113 

• Washington State: Department of Ecology: American Waterweed - A Common Native Plant 

http://www.ecy.wa.gov/programs/wq/plants/native/elodea.html 

• Washington State: Department of Ecology: Submersed plants: Elodea canadensis. 

http://www.ecy.wa.gov/programs/wq/plants/plantid2/descriptions/elocan.html

http://www.ecy.wa.gov/programs/wq/plants/plantid2/photopages/photo_elodea.html 

• US Dep. of Agriculture: Natural Resources Conservation Service: Canadian waterweed 

http://plants.usda.gov/java/profilesymbol=ELCA7 

• Aquatic Plants of the North (Minnesota, USA): Canadian waterweed 

http://www.rook.org/earl/bwca/nature/aquatics/elodeacan.html 

• Walking among the S-weeds: Elodea canadensis 

http://www.s-weeds.net/familjer/monocots/alismatales/elodeacan.html 

FIND OUT MORE: Nuttall's waterweed (Elodea nuttallii) 

• Swedish Museum of Natural History: (Virtual flora): Smal vattenpest (Elodea nuttallii) 

In Swedish only 

http://linnaeus.nrm.se/flora/mono/hydrocharita/elode/elodnut.html 

• North European and Baltic Network on Invasive Alien Species (Nobanis): Elodea nuttallii 

http://www.nobanis.org/speciesInfo.asptaxaID=4046 

• European Nature Information System Database (EUNIS): Elodea nuttallii 

http://eunis.eea.europa.eu/species-factsheet.jspidSpecies=186344&idSpeciesLink=186344 

• Aquatische Neopyhten in Nordrhein-Westfalen: Elodea nuttallii 

http://www.aquatischeneophyten.de/Webseiten%20NEU/Pflanzenseiten%20neu/Elodea%20nuttallii.htm 

• Ulster Museum Sciences Division: Flora of Northern Ireland: Elodea nuttallii 

http://www.habitas.org.uk/flora/species.aspitem=2115 

• Washington State: Department of Ecology: American Waterweed - A Common Native Plant 

http://www.ecy.wa.gov/programs/wq/plants/native/elodea.html 

• Washington State: Department of Ecology: Submersed plants:.Elodea nuttallii 

http://www.ecy.wa.gov/programs/wq/plants/plantid2/descriptions/elocan.html 

http://www.ecy.wa.gov/programs/wq/plants/plantid2/photopages/photo_elodeanuttallii.html 

• Aquatic Plants of the North (Minnesota, USA): Western waterweed 

http://www.rook.org/earl/bwca/nature/aquatics/elodeanut.html 

• Aquatic Weed Control LLC: Elodea canadensis. Elodea nuttallii 

http://www.awc-america.com/plant_id_utility/plants/elocan.html 

• Walking among the S-weeds: Elodea nuttallii 

http://www.s-weeds.net/familjer/monocots/alismatales/elodeanutt.html 

PHOTO CREDIT 

© Armin Jagel 

http://www.botanik-bochum.de/ 

• This factsheet on Elodea canadensis and Elodea nuttallii was created on 1 September 2006 

• First update: 6 November 2006 

• Translated by Martin Naylor on 1 December 2006 

• Second update ("Find out more" only): 16 December 2006

Elodea nuttallii

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