Invasive Species Eradication Project 2021-2025

Our award-winning Canal & River Invasive Species Eradication Project focused on tackling four priority invasive plants that are damaging canals, destroying habitats and harming wildlife.

Read the video transcript
In between Dudley and Stourbridge, a battle is underway removing an invasive plant that is choking our waterways.
This sort of species of weed is very knotty and sticks together, but it’s one of the harder ones to get out.
This is floating pennywort. So, floating pennywort originates from the Americas, predominantly South America. It was introduced into the UK around the 19th century. The big problem with floating pennywort is that it grows very rapidly. It can grow up to 20 centimetres a day. But also, it can clog waterways, it can impact native wildlife and cause issues for navigation as well on our canals.
In a few weeks time, the team will return. If they miss even the smallest scrap of pennywort, the plant can quickly regrow and leave you back at square one, but that’s what’s different about this £600,000 project. It’s not just about controlling these four invasive species – giant hogweed, Japanese knotweed, floating pennywort, and water fern or Azolla – it’s about eradicating them completely, and to do that, you can physically pull out things like floating pennywort that’s what they’re doing here. Some of the other plants, you inject weed killer directly into their stems or destroy them with electricity and then for things like Azolla, you actually release a weevil that eats the plant and kills it that way.
The work is funded by water company Severn Trent and it doesn’t just benefit boat owners and wildlife.
Some species of invasive non-native species can cause water quality to decrease, so by removing some of these species, we can increase our water quality and that reduce the number of chemicals we use at our treatment plants and that reduces our operating costs, then in turn that can help reduce our customer bills.
Right across the Midlands, war has been declared on these plant pests.
David Gregory Kumar, BBC Midlands Today, Brierley Hill.

Why was the INNS eradication project necessary?

Invasive non-native species are one of the largest global threats to biodiversity, and our canals and rivers.

Japanese knotweed, giant hogweed, floating pennywort and water fern (Azolla) can grow at rapid speed, often from the most minuscule of fragments. This makes them costly and challenging to remove completely. Without regular and effective management, their dominating presence could cause irreversible damage to the fragile ecosystems of our waterways.

Funded by Severn Trent's Great Big Nature Boost Scheme, this four-year project enabled us to trial ground-breaking methods of eradication to find more sustainable, cost-effective and longer-lasting solutions.

What did the project involve?

Throughout the four years, our team implemented key phases from contractor surveying through to the deployment of new eradication techniques, as well as regular monitoring and evaluation processes.

We were able to attempt first-of-a-kind trials, including an eco-friendly dredging, hessian matting and hydroseeding process on Himalayan balsam found at the Penarth Feeder, which reduced the need for further treatment by 90%.

After many years of research alongside CABI, we were able to use weevils to help eradicate floating pennywort and water fern. These plant-munchers effectively reduced vast quantities in a matter of weeks, offering a natural alternative to chemical sprays.

Vital research conducted on the impacts of water and sediment quality on the presence of algae and invasive macrophytes (aquatic plants) will also enable us to shape future biocontrol strategies effectively.

A moorhen and two chicks peck at green water fern covering the surface of the canal

Why are invasive plant species a problem?

Find out more about how invasive plants harm canals, impact native wildlife and destroy habitats, and what you can do to help prevent their spread

Project achievements

Other areas of success include:

Eradication of invasive plant species from 313km of waterway
Aquatic weed management via mechanical removal across 108km of waterways
Targeted treatment in over 300 land-based invasive species sites
Successful one-of-a-kind trials of Himalayan Balsam in two sites
One of, if not the, largest floating pennywort removal exercises - resulting in 1,500 tonnes removed across 35km
Biocontrolled deployment of weevils across 22 sites, many with multiple release locations
Evidence that weevils persisted for consecutive years in some areas, prompting a return of native water cress

What impact does this project have on the future?

Our work to tackle invasive species is not over.

The team will participate in National Floating Pennywort strategy groups to build on our successes and identify additional opportunities to tackle this particular plant.

With a largely successful weevil release, we will also continue this eradication method across all regions, and monitor the progress. It is evident that climatic factors such as air and water temperature have a significant impact on the successful overwintering and feeding activity of the weevils, and this must be a key consideration on both invasive plant growth and the biocontrol methods that are used to eradicate them.

Before and after: eradicating invasive aquatic species

Witness the transformation and discover how much floating pennywort and water fern we are extracting from our waterways

Award-winning work

This £600,000 project was the largest invasive species eradication project on UK inland waterways.

It covered a significant geographical area spanning the West Midlands, East Midlands, Wales & South West, Yorkshire & North East, and North West regions.

We are delighted to have won the NGO Impact Award 2022 award from the Chartered Institute of Ecology & Environmental Management (CIEEM) for this project. This award recognises the achievement of NGOs in delivering an initiative that has had a major impact in benefitting nature and society.