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Curly Waterweed - Invasive Species Information

What Is Curly Waterweed - (Lagarosiphon major)?

Habitat: Aquatic, fresh water
Distribution in Ireland: Sparse distribution but locally abundant in some places

Status: Established
Family name: Hydrocharitaceae

Reproduction: All reproduction is by fragmentation or vegetative reproduction.  Detached stems, when they sink, root from the nodes and establish new populations

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Curly Waterweed - (Lagarosiphon major)

Curly Waterweed

Originally from Southern Africa, where it is regarded as a nuisance weed. 

The plant can grow in water up to 6m deep. 


Curly waterweed is a perennial, submerged dioecious plant with branched stems and strongly recurved leaves alternate or spiralled or rarely in whorls up the stem, with two rows of fibre-like cells on the margins with > 50 teeth on each side.


It occurs in still or very slow-flowing water, principally in eutrophic, calcareous canals, ponds, lakes and gravel pits. 

How To Identify Curly Waterweed?

Leaves: Strongly recurved dark green leaves borne in a spiral arrangement, slight yellow tinge from the underside. 

Stem: The long stem is brittle and easily broken (aiding dispersal).

Size: Can grow in water up to 6 metres deep 

Curly Waterweed Leaf
Lough Corrib Ireland After Infestation
Lough Corrib Ireland Before Infestation
Curly Waterweed - Lagarosiphon major ID Guide

Curly Waterweed - Lagarosiphon major ID Guide

Lough Corrib Ireland Before Infestation

Lough Corrib Ireland After Infestation

Curly Waterweed Leaf

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Why Is Curly Waterweed A Problem?

Plant stands produce dense canopy vegetation on the water surface and displaces native species. 


In high densities it blocks light from penetrating the water leading to a disturbance in the food web and a decrease in biodiversity.


It interferes with commercial navigation and water-based recreation. It has a negative impact on some native fish species. Native macroinvertebrate community structures are altered. 

National Biodiversity Data Centre Ireland - Recognised Invasive Plant Species.


There are currently 35 invasive plant species identified as high risk on Ireland's biodiversity control list. Here's the A to Z of plant species included on the list (updated 2017)...

Click on a species from the following list to find out more

  1. American Skunk-CabbageLysichiton americanus

  2. Brazilian Giant-RhubarbGunnera manicata

  3. Broad-Leaved RushJuncus planifolius

  4. Cape PondweedAponogeton distachyos

  5. Cord-GrassesSpartina (all species and hybrids)

  6. Curly Waterweed - Lagarosiphon major

  7. Dwarf Eel-GrassZostera japonica

  8. FanwortCabomba caroliniana

  9. Floating PennywortHydrocotyle ranunculoides

  10. Fringed Water-LilyNymphoides peltata

  11. Giant HogweedHeracleum mantegazzianum

  12. Giant KnotweedFallopia sachalinensis

  13. Giant-RhubarbGunnera tinctoria

  14. Giant SalviniaSalvinia molesta

  15. Himalayan BalsamImpatiens glandulifera

  16. Himalayan KnotweedPersicaria wallichii

  17. Hottentot-FigCarpobrotus edulis

  18. Japanese KnotweedFallopia japonica

  19. Large-Flowered WaterweedEgeria densa

  20. Mile-a-Minute WeedPersicaria perfoliata

  21. New Zealand PigmyweedCrassula helmsii

  22. Parrots FeatherMyriophyllum aquaticum

  23. Red AlgaGrateloupia doryphora

  24. RhododendronRhododendron ponticum

  25. SalmonberryRubus spectabilis

  26. Sea-Buckthorn Hippophae rhamnoides

  27. Spanish Bluebell Hyacinthoides hispanica

  28. Three-Cornered LeekAllium triquetrum

  29. WakameUndaria pinnatifida

  30. Water ChestnutTrapa natans

  31. Water FernAzolla filiculoides

  32. Water LettucePistia stratiotes

  33. Water-PrimroseLudwigia (all species)

  34. WaterweedsElodea (all species)

  35. WireweedSargassum muticum

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