The Rivers Trust warns alien invasion is destroying native biodiversity and costing Irish economy over 200m per year

To mark Invasive Species Week (May 15th to 21st), The Rivers Trust is calling on everyone to play their part in the war against alien invaders that are costing not just the loss of biodiversity but also hundreds of millions of euros annually to the Irish economy. 

Matthew Woodard


The Rivers Trust All-Ireland Director Mark Horton said: “We are using this opportunity to raise awareness and encourage actions to prevent the introduction and spread of non-native plants, animals, insects, and microscopic organisms. We are calling on everyone to play their part in the continual battle against alien invaders, which is inflicting high costs across Ireland without receiving the attention it deserves.”

Invasive species are non-native organisms that are introduced to an area and have a negative impact on the native species and environment. They are one of the top five drivers of global biodiversity loss and cost the Irish economy approximately €202,894,406 a year and, in some cases, can even harm human health. 

Negative impacts of invasive alien species on biodiversity occur through competition, herbivory, predation, alteration of habitats and food webs, the introduction of parasites and pathogens, and the dilution of native gene pools. On the island of Ireland, the most negative impact is direct competition with native biodiversity, whilst alteration to habitats and the spread of parasites and pathogens (especially to native fish populations) are also significant threats. 

The Corbicula clam is an example of a relatively new invader posing a serious threat to Ireland’s wild Atlantic salmon river spawning beds. It is so well adapted that it resembles gravel on a riverbed and can reproduce without a mate. Apart from potential damage to the spawning of salmon and brown trout, it can also interfere with the operation of power plants, drinking water abstraction and other industries using raw water. Labelled the “most notorious” invasive species in the world, it has been present in Europe for the past 50 years and may have made its way to Ireland through the aquarium trade. It was first detected in the river Barrow in April 2010 and has spread to the Nore, the Foyle, and the Shannon rivers, where leisure craft can help its distribution.

clam clam

Mark said: “Water is an ideal transport medium for the dispersal of many of these invasive species. Rivers and loughs with their banks and shorelines are amongst the most vulnerable areas to their introduction, spread and impact. That’s why local River Trusts across Ireland are continually working on the ground to monitor and control the thousands of types of invasive species destroying freshwater habitats, including rivers, lakes, and loughs.”

The Rivers Trust Ireland Development Manager Constanze O’Toole said: “Last summer, Maigue Rivers Trust in Co Limerick co-ordinated the professional removal of over 6km of Giant Hogweed which is choking the Morningstar River. This work removed an estimated six million Giant Hogweed seeds. This plant is not only invasive, but its sap can cause severe burns to the skin.”

Funded by the Local Authority Waters Programme (LAWPRO), Maigue Rivers Trust created a management strategy for initial monitoring and removal. However, Giant Hogweed control must be a multiannual project and will need intervention for at least five years for the Morningstar River until the plant’s seed bank is exhausted. Because of the toxic nature of this invasive species, this work needs expensive specialist contractors, so future funding and investment are now required to continue the necessary control work.

Inishowen Rivers Trust in Donegal has been actively removing (where safe) invasive species such as Japanese Knotweed and Rhododendron from riverbanks. Inishowen Rivers Trust has also been educating the local community and recruiting volunteers called River Guardians to record and monitor invasive species in the catchment. Members aim to map the distribution of these species around Inishowen - particularly those found on riverbanks where they can cause bank erosion.

“Prevention is an essential aspect of controlling invasive species. Monitoring and early detection can help prevent invasive species' establishment and spread. Water users need to thoroughly clean boats, canoes, paddle boards, and fishing equipment including waders before entering waterways, and disposing of waste and ballast water properly. Follow the guidelines recommended by the Check, Clean and Dry campaign,” Constanze said. 

“Once established, invasive species are extremely difficult and costly to control and eradicate, and their ecological effects are often irreversible. The current threats posed by invasive species in Ireland are very significant, and it is critical that we take this issue seriously. This is a complex problem and requires multi-agency intervention. It also takes action and vigilance from the public as invasive species are often introduced by accident.”

The predictions for future invasive species arriving in Ireland include Salmon Fluke, which can devastate salmon populations. In recent decades, this parasite has caused at least €2.5 billion in economic impacts. With the Irish salmon angling industry valued conservatively at €11 million in 2003 and the associated enormous natural capital value of this iconic species, the loss of Atlantic salmon in Ireland would be a significant loss in terms of biodiversity, heritage, and economy. Cost-efficient, sustained, and effective biosecurity would minimise the risk of this and other invaders arriving in Ireland.

The impact of invasive species is not just an issue for biodiversity. Invasive species affect vital economic sectors such as agriculture, tourism, and the construction sectors. However, these economic impacts are often overlooked or under-reported.

Shockingly, the current estimated annual cost of invasive species to the economies of Ireland and Northern Ireland is €202,894,406 and £46,526,218 (€58,623,034), respectively. The combined estimated yearly cost of invasive species in both economies is €261,517,445 (£207,553,528). In Great Britain, invasive alien species are estimated to cost the economy at least £1.7 billion each year.

“New economic analysis by An Fóram Uisce indicates that if we don’t tackle the issue effectively and with urgency, the costs to Ireland of invasive species will rise to €26.5 billion per year by 2030 for all invasives, with aquatic and semi-aquatic invasives alone projected to cost over €3.8 billion per year.

Mark concluded: “With so much at stake, The Rivers Trust is calling for better investment, more research and a clear and effective biosecurity strategy for Ireland that includes public education and awareness programs and funding for community involvement which is the only way to tackle this ongoing and widespread threat to human health, biodiversity and the Irish economy.”

If you encounter an invasive species, please report it online at

Back to top