Most Unwanted: Nuttall's waterweed
Elodea nuttallii
Habitat: Freshwater
Threat: Clogs waterways
Status: Established
Elodea nuttallii originated from North America. This species is very similar to another invasive specie know as Elodea canadensis (Canadian waterweed). Both species grow in still or slow flowing eutrophic waters but Elodea nuttallii has replaced E. canadensis at many sites possibly due to increased eutrophication. E. nutallii is most common in calcareous waters and eutrophic waters because it has a high tissue demand for both phosphorus and nitrogen.
What is it?
This is an aquatic weed that grows rapidly towards the surface of eutrophic freshwater systems without branching where they form a densely branched canopy. It over winters in Ireland as horizontal shoots which regenerate new lateral shoots as the temperature reaches 6-8oC.
Both invasive species of Elodea are very similar in appearance. Both are dark green in colour and it may be quiet difficult for a member of the public to distinguish these species. Both Elodea species have whorls of three leaves around the stem. The size and shape of the leaves are used in identification to species level. For more information please see the CEH Information Sheet 25: Elodea nuttallii.
Impact
E. nuttallii tends to dominate native macrophyte communities which may lead to there local extinction. Impacts have also been recorded on invertebrate communities. This species may also have a significant impact on protected sites.
E. nuttallii is also known to replace other invasive species as the dominant species in an impacted ecosystem. More recently data from Britain suggests that this species is now becoming replaced by Largarosiphon major. All Elodea species tend to take up metals from the sediment and releasing them into the water. E. nuttallii is very tolerant of Copper in particular.
Where is it from?
This species is native to North America but is now invasive in Britain where it is common.
Where are they in Ireland?
This specie now occurs at a number of sites spread right across the island.
How did it get here?
Traded as a garden plant.
How is it spreading in Ireland
Escape from garden ponds.
Disposal of garden waste near water ways.
Potential for spread by birds and animals.
What you can do
Do not buy invasive aquatic plants.
Dispose of garden waste in a responsible manner.
Report all sightings.
Additional reading
Habitas Invasive Alien Species in Northern Ireland
