Nuttall’s waterweed is an aquatic weed native to North America that has become relatively widespread in freshwaters across the country. It is a member of the Hydrocharitaceae family and is commonly found in species poor macrophytes communities and where boat traffic is prolific. It can form dense mats and acts as a metal ion pump that takes metal ions up from the sediment and releases them into the water. It is especially tolerant of copper. It is common in eutrophic and calcareous waters due to its high tissue demand for nitrogen and phosphorus.
Nuttall’s Waterweed (Elodea nuttallii)
Classified as a high impact invasive species by the Irish National Biodiversity Centre. Third Schedule listed species under Regulations 49 & 50 in the European Communities (Birds and Natural Habitats) Regulations 2011.
- Leaves are narrower than 1.75mm, not longer than 10mm and the leaves are folded over in the middle. They are pale green and lanceolate. Often twisted or curled.
- Leaves are arranged in whorls of 4 around the stem
- Similar to Elodea canadensis
Only female Nuttall’s waterweed is found in Ireland so spread of Nuttall’s waterweed occurs solely from fragments which are easily transported by currents and wildlife to colonise new areas. As such, the spread of Nuttall’s waterweed is rapid.
- Forms dense carpets on lakes and reservoirs that restrict boat movements and fishing
- Blocks out light and outcompetes native plant species
- Block pipes and drains
- Increase flooding
- Mechanical: The best option for control of Nuttall’s waterweed. Treatment can be carried out using a specialised boat or trailing V blades or chains that mechanically cuts and pulls up the waterweed. This causes the vegetation to float to the surface where it can be collected with nets. The waterweed can then be composted on dry land. This action should be treated at 6–8-week intervals starting in February and should be continued over the summer months before September, where the plant reaches maximum biomass.
- Biological: Blocking the light with mats or sheeting can be an effective way of controlling Nutall’s waterweed. This can also kill off native plants but can facilitate the regeneration of native plants from seed reserves.
- Chemical: Chemical herbicide is not viable.
(National Biodiversity Data Centre, Ireland, Nuttall’s Waterweed (Elodea nuttallii), image, accessed 27 June 2022)