Elodea canadensis | Canadian Waterweed | Tím uisce
Listed as a schedule 9 species under Articles 15 & 15A of the Wildlife Order (Northern Ireland) 1985 (Article 15A not yet enacted).
First reported in the wild
Invasive species - risk of High Impact
Introduction pathways - 1
Escape from Confinement
Introduction pathways subclass - 1
NAPRA Ireland risk assessed
Yes. This species underwent a Non-native species APplication based Risk Analysis in 2014.
Overall risk of this species to Ireland is categorised as: MINOR with a HIGH level of confidence.
Overall conclusion summary: As Elodea canadensis is now now rarely a problematic organism within the water bodies in Ireland, it is unlikely to cause any further negative impacts except under certain circumstances (e.g. in localised parts of disturbed, artificial or newly introduced habitats).View the full risk assessment:
Submerged, aquatic plant, anchored in the substrate. Stems long, branched and up to 3m long, leaves minutely serrated and in whorls of 3, leaves wider than E. nuttalli (Stace, 1997).
Has gone through a pattern of colonisation and then rapid expansion, during which time the plant formed dense mats and was problematic, before declining and naturalising (Simpson, 1984). While in part it was displaced by Elodea nuttalli (Simpson, 1984) and possibly other invasive aquatic plants, this pattern of invasion may be typical of this plant across both its invaded and native range (Simberloff & Gibbons, 1994). However while it currently has no negative impacts on native fauna, alterations to the native biotic communities may have occurred during the expansion phase that were not documented at the time, similar to those observed currently in E. nuttalli (Kelly et al., 2015).
Inland surface waters; Estuaries
All reproduction in Elodea spp in the British Isles is through vegetative means, as only female plants are present (Simpson. 1984).
Pathway and vector description
Elodea canadensis is sold as an oxygenator/ornamental weed and kept in artificial watercourses, garden ponds and aquaria, from where it is introduced into the wild, either accidentally through flooding or waterfowl or deliberately by dumping of plant material into water courses (Millane & Caffrey, 2014).
Mechanism of impact
Lakes, rivers, canals & other slow moving waterbodies.
Established - Common. Found through out the country, formerly highly abundant and over growing areas, has since been naturalised (Millane & Caffrey, 2014). This is similar to the pattern of spread in Britain (Simpson, 1984) and this pattern of colonisation, rapid expansion and then gradual decline and possible local extinction appears to be repeated across its introduced range (Simberloff & Gibbons, 2004).
Native to North America.
Date of first record category
Fifty year date category
Records submitted to Data Centre in 2022
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How can you help
Report any sightings to the National Biodiversity Data Centre. Do not purchase or plant in your garden. Dispose of garden waste and nuisance plants responsibly.
Delivering Alien Invasive Species In Europe (DAISIE) project list this as one of the 100 Worst Invaders in Europe.
Reynolds, S.C.P. (2002) A catalogue of alien plants in Ireland. National Botanic Gardens. Glasnevin, Dublin. Stace, C. (1997). New Flora of the British Isles 2nd Edition. Cambridge University Press, Cambridge. Millane, M. & Caffrey, J. (2014). Risk Assessment of Elodea canadensis Michaux – Canadian Pondweed. Prepared for Inland Fisheries Ireland and the National Biodiversity Data Centre. Simpson, D. A. (1984). A short history of the introduction and spread of Elodea Michx in the British Isles. Watsonia, 15(1), 1-9. Simberloff, D., & Gibbons, L. (2004). Now you see them, now you don't!–population crashes of established introduced species. Biological Invasions, 6(2), 161-172. Kelly, R., Harrod, C., Maggs, C. A., & Reid, N. (2015) Effects of Elodea nuttallii on temperate Freshwater plants, microalgae and invertebrates: small differences between invaded and uninvaded areas. Biological Invasions, 1-16.