Lagarosiphon major | Curly Waterweed



Conservation status

Least Concern

Legal status

Third Schedule listed species under Regulations 49 & 50 in the European Communities (Birds and Natural Habitats) Regulations 2011. (Note: Regulation 50 not yet enacted).

Listed as a schedule 9 species under Articles 15 & 15A of the Wildlife Order (Northern Ireland) 1985 (Article 15A not yet enacted).

Regulated invasive  species of Union concern under the European Regulation on the prevention and management of the introduction and spread of invasive alien species [1143/2014].

Native status


First reported in the wild



Invasive species - risk of High Impact

Irish status


Introduction pathways - 1

Escape from Confinement

Introduction pathways subclass - 1

Pet/aquarium species

Introduction pathways - 2

Escape from Confinement

Invasive score


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: MAJOR with a VERY HIGH level of confidence.

Overall conclusion summary:  Experience of the invasion of Lough Corrib by Lagarosiphon major (where over 92 hectares of the lake became infested [Caffrey et al. 2011]) clearly indicates that this invasive species has the potential to cause significant ecological, environmental and socio-economic impacts should it become established in other natural freshwaters in Ireland.

 View the full risk assessment:

Species Biology


Submerged, aquatic plant, anchored in the substrate. Stems up to 3m long, tends to from dense stands, leaves strongly curve, 6-30mm long, 1-3mm wide (Booy et al., 2015). Can be confused with Elodea spp., Egeria densa, and Hydrilla verticillata.


Grows densely dominating the substrate and excluding native vegetation (Caffrey et al., 2010). By altering the habitat it alters the macroinvertebrate community in the area (Caffrey et al., 2010), which may impact on higher trophic levels. Management in Lough Corrib, using biodegradable jute matting has been used to remove L. major and restore native macrophytes (aquatic plants large enough to be visible to the naked eye) (Caffrey et al., 2010). A study comparing competition between invasive species found that L. major is outcompeted by Egeria densa in warmer waters, but outcompetes in colder, shallower waters which may impact on the distribution and invasion pattern of both species in Ireland (Riis et al., 2012).


Inland surface waters


As plants outside its native range to date have been female it reproduces solely by fragmentation and vegetative reproduction (Cook, 1982 in Caffrey et al., 2011).

Pathway and vector description

Sold as an ornamental or oxygenating plant in ponds or aquaria, it is present in outdoor ponds and artificial lakes (Caffrey et al., 2011), and was introduced into the wild in Ireland either as a result of flooding washing the plant into waterways or deliberate dumping. Subsequently spread vegetatively on boats, angling equipment and by natural means.

Mechanism of impact

Competition, Bio-fouling

Management approach

There is currently an EU wide ban on the sale, growing and keeping of this plant (European Commission, 2017).

Control of Lagarosiphon major has proved difficult due to its aggressive growth rates and ability to out compete native species (Caffrey & Acevedo, 2008).


Hand-picking is the most effective method for small infestations (<1m²) provided all rhizoids are removed (CAISIE, 2013).


The use of a V-blade trailed behind a boat, which tears the plant out at the root was shown to be successful in controlling L. major at Lough Corrib (Caffrey & Acevado, 2008). A containment net should be used to catch any loose fragments (CAISIE, 2013).


Benthic barriers (jute mats) can be used for control of infestations from 1 – 1000m² (CAISIE, 2013). Using jute mats rather than plastic sheeting has the advantage of allowing the germination of the seeds of native plant species (Caffrey, 2010). For stands in shallower water (<1m) a double layer of matting is more effective (CAISIE, 2013).

Broad environment


Habitat description

Anchors in the substrate of lakes and slow moving rivers (Booy et al., 2015)

Species group


Native region


Similar species

Elodea spp., Egeria densa


World distribution(GBIF)

Irish distribution

Established - Widespread & Locally abundant. Particularly abundant in the upper lake of Lough Corrib, where in 2008 it occupied ~92ha of lake bed (Caffrey et al., 2011).

Native distribution

Native to Africa (Booy et al., 2015).

Temporal change

Date of first record category


Fifty year date category


Records submitted to Data Centre in 2024

The following map is interactive. If you would prefer to view it full screen then click here.

How can you help

Report any sightings to the National Biodiversity Data Centre. Practice good biosecurity protocols when moving boats and fishing equipment by thoroughly disinfecting all gear. Do not purchase Lagarosiphon major or Elodea crispa (a commercial name for L. major). Do not dump aquatic plants in waterways or stock non-indigenous aquatic plants in outdoor ponds or lakes.



Booy, O., Wade, M. & Roy, H. (2015) Field Guide to the Invasive Plants & Animals in Britain. Bloomsbury.

Caffrey, JM and Acevedo, S. (2008). Lagarosiphon major in lough corrib – management options. In: Moriarty C, Rosell R, Gargan P (eds), Fish Stocks and their Environment. Institute of Fisheries Management, Westport, Co Mayo, pp 85-97 Site accessed 28 August 2017.

Caffrey, J. M., Millane, M., Evers, S., Moron, H., & Butler, M. (2010). A novel approach to aquatic weed control and habitat restoration using biodegradable jute matting. Aquatic Invasions, 5(2), 123-129.

Caffrey, J., Millane, M., Evers, S., & Moran, H. (2011). Management of Lagarosiphon major (Ridley) moss in Lough Corrib—A review. In Biology and Environment: Proceedings of the Royal Irish Academy (pp. 205-212). Royal Irish Academy.

Control of Aquatic Invasive Species and Restoration of Natural Communities in Ireland (CAISIE). (2013). Best practice control measures for Curly-leaved waterweed Lagarosiphon major. EU LIFE+ Project Site accessed 28 August 2017.

Cook, C.D.K. 1982 Pollination mechanisms in the Hydrocharitaceae. In: J.J. Symocns, S.S. Hooper and P. Compere (eds), Studies on aquatic vascular plants, 1-15. Brussels. Royal Botanic Society of Belgium.

European Commission. (2017). Invasive Alien Species of Union Concern. European Union, Luxembourg.

Reynolds, S.C.P. (2002) A catalogue of alien plants in Ireland. National Botanic Gardens. Glasnevin, Dublin.

Riis, T., Olesen, B., Clayton, J. S., Lambertini, C., Brix, H., & Sorrell, B. K. (2012). Growth and morphology in relation to temperature and light availability during the establishment of three invasive aquatic plant species. Aquatic Botany, 102, 56-64.

Global Invasive Species Database

CABI Datasheet

IUCN Red List of Threatened Species