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Stop the spread of Lagarosiphon major

Curley leaved waterweed (Lagarosiphon major)is a major threat to Ireland's watercourses.

The weed

  • Aggressive, invasive, alien plant species that originated in Southern Africa, where it is regarded as a nuisance weed.
  • The plant can grow in water up to 6m deep.
  • In addition to occupying the full water column, plant stands produce dense vegetation on the water surface.
  • The leaves are strongly recurved and are borne in whorls of 3 or in a spiral arrangement.
  • The long stem is brittle and easily broken (aiding dispersal).
  • Only female plants are present and all reproduction is by fragmentation or vegetative reproduction.
  • Detached stems, when they sink, root from the nodes and establish new populations.


Brochure page: Lagarosiphon major rooting plant fragment

The Problem

  • Currently, in Ireland, we are at an early stage in infestation; however, significant weed stands exist in Lough, Corrib.
  • Forms very dense infestations in suitable habitats
  • Capable of occupying the full water column inwaters up to 6m deep.
  • Stems are easily broken and disperse rapidly.
  • Dramatically alters the ecology for native plants, insects and fish
  • Creates a poorer ecosystem for native plants, insects and fish
  • Poses a serious threat for tourism, angling, boating and other recreational pursuits.
  • Can cause fish kills through oxygen depletion
  • Potentially a more major threat than the Zebra mussel.


Brochure page: 26 acres of Rinneroon Bay, Lough Corrib, overgrown with Lagarosiphon major.

The Cause

  • Sold by garden centres as an oxygenating plant.
  • Spread by fragmentation via wind dispersal, boat movement, angling equipment and, possibly, waterfowl.



  • An expert group with international experience in aquatic weed management has been convened to determine and implement all possible options for the control and elimination of Laragosiphon major.


The habitat

  • The weed will grow in lakes rivers streams, canals and ponds.


Brochure page:  Lagarosiphon major (right) is similar to Elodea canadensis

To stop the spread


  • Always thoroughly clean your
    angling equipment
    and waders

    when leaving the waterway.


  • Introduce any weed to any watercourse.
  • Dispose of invasive plant material in the vicinity of any watercourse.
  • Drive boats through established stands.


How can you help?

If you see this plant please immediately inform:

Dr. Joe Caffrey,
Central Fisheries Board.



This brochure was produced with assistance from the Western Regional Fisheries Board, the National Parks and Wildlife Service and Galway County Council.

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