The Rivers Trust warns alien invasion is destroying native biodiversity and costing Northern Ireland economy £46.5m 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 tens of millions of pounds annually to the local 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, inflicting high costs in many areas in Northern 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 Northern Ireland economy approximately £46.5 million 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.

An example of an invasive species which, over the last number of decades, has impacted both biodiversity and the economy in Northern Ireland is the zebra mussel. Native to the Caspian and Black Seas south of Russia and Ukraine, this freshwater mussel was first detected in Lough Derg on the Lower Shannon in 1997, although it is believed that they arrived after being accidentally introduced to Ireland on the hulls of imported second-hand boats.

Zebra mussels attach to hard surfaces in rivers and lakes, including rocks, anchors, boat hulls, intake pipes, unionid mussels and plants. These invaders have already driven our native swan mussel populations in Lough Erne, Lough Derg, Lough Key and Lough Ree to near extinction. They have also impacted water abstraction stations on Lough Erne; in one case, it cost more than £100,000 to modify the state-of-the-art Killyhevlin Water Treatment Plant because of this alien invader.

“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 Rivers Trust across Northern Ireland and Ireland are continually working on the ground to monitor and control the thousands of invasive species destroying freshwater habitats, including rivers, lakes, and loughs. Works to remove invasive species such as Japanese Knotweed, Giant Hogweed and Himalayan Balsam, which are choking miles of riverbanks and destroying critical spawning habitat for trout and salmon, are time-consuming and very expensive as it often involves specialist contractors,” Mark said.

“Prevention is an essential aspect of controlling invasive species. Measures such as monitoring and early detection can help prevent invasive species' establishment and spread. The public can also help by not releasing pets or exotic plants into the wild, thoroughly cleaning boats, canoes, paddle boards, and fishing equipment before entering waterways, and disposing of waste properly.

“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 Northern 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 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 estimated annual cost of invasive species to the economies of Ireland and Northern Ireland is £161,027,307 (€202,894,406) and £46,526,218 (€58,623,034) respectively. The combined estimated annual cost of invasive species in both economies is £207,553,528 (€261,517,445). *

In Great Britain it is estimated that invasive alien species cost the British economy at least £1.7 billion each year. Forecasts indicate the costs of invasive species are likely to rise as more species arrive each year and species that are already present become invasive or more widespread.

Mark concluded: “With so much at stake, The Rivers Trust is calling for investment and a clear and effective biosecurity strategy for Northern 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 Northern Ireland economy.”

If you encounter an invasive species, you can record it on the iRecord App, CEDaR , or iNaturalist. Invasive Species NI will use the information to inform landowners of their legal obligation to manage invasive species on their property.

Back to top