The Issue

Invasive non-native species are animals or plants which have not colonised naturally, but have been introduced (accidently or deliberately) by people and now have the ability to pose a threat to the environment, economy or people. Currently, there are 3248 non-native species established in the UK but not all of these are invasive. Around 15% of these plants and animals pose a threat to the way we live and once established, their damage is irreversible. INNS threaten to reduce biodiversity, spread disease, modify ecosystems, drastically reduce and alter native populations across GB if left unchecked, unmanaged and uncontrolled. The number of INNS in the UK will increase with climate change bringing about an elevated risk due to warmer winters, increased flooding and altered species ranges which will bring greater pressure on GB freshwater systems.

INNS impact us through:

  • Costing the UK economy around £1.8 billion a year through causing damage to structures and roadways, dominating rivers and causing erosion. Japanese knotweed can cause huge damage to man-made structures like building foundations and tarmac roads.
  • Being one of the top five drivers of biodiversity loss, leading to the dramatic decline of native wildlife such as white-clawed crayfish and the tansy beetle. The tansy beetle was originally widespread across Britain yet with the introduction of Himalayan balsam, which outcompetes tansy, the beetle’s supply of food and shelter, the tansy beetle has been restricted to two populations in the UK.
  • Threatening the survival of rare native species and outcompeting plant life in fragile ecosystems such as wet woodlands and freshwaters. American skunk cabbage outcompetes mosses and lichens in wet woodlands, reducing biodiversity in these rare environments.

What we’re doing

Across WCRT there are a number of INNS present and we work to manage these species wherever we can, as left unmanaged they can reduce habitat resilience through increasing erosion which increases sediment, nutrient and pollutant input into streams. This can have damaging impacts for spawning fish, increase flood risk and decrease the overall biodiversity of these ecosystems.

This project focuses primarily on the Derwent Catchment, encompassing the tributaries of the Upper Derwent, Glenderamackin, St. Johns Beck, Greta, Middle Derwent, Cocker, Lower Derwent and the Marron. The 679km2 Derwent catchment includes multiple SACs and SSSIs and 64% of the catchment falls within the Lake District National Park, a UNESCO World Heritage Site that attracts 17 million visitors a year, putting it at greater risk of introduced species from elsewhere in GB and across the world.

Long Term Management

WCRT have had a programme of INNS control since the beginning of the Trust, with long-term control projects of Himalayan balsamJapanese knotweed and American skunk cabbage. In 2022, WCRT treated over 30ha of these three INNS, with over 990 volunteer hours going into the project from June-August. Whilst WCRT have not always had the resources to manage INNS, we have always kept records of INNS in the catchment, wherever they may be, so that when funding becomes available we can tackle INNS strategically.

The Derwent INNS Project today

The threat of INNS has been addressed globally, nationally and regionally and in 2023, WCRT have tackled it locally with the creation of the Derwent Invasive Non Native Species Strategy, which outlines actions for the following five years to be taken by both WCRT and partners. The main aim of the INNS Derwent project is:

To develop and maintain cost-effective sustainable strategic approaches to prevent, detect, control and eradicate specified Invasive Non Native Species in the Derwent Catchment through a uniform, catchment-based approach across partners through prevention, surveillance, early detection, monitoring, rapid response and long-term management.

The strategy puts an emphasis on long term management which WCRT have always maintained and whilst the strategy aims to increase this management, it also puts an emphasis on prevention and awareness spreading to prevent any INNS from becoming established in the catchment.

How you can help:

  • Learn about biosecurity, and make sure you Check, Clean, Dry your clothes, equipment and footwear every time you leave the water
  • Learn to spot invasive species and Be Plant Wise - 60% of invasive plants come from horticulture
  • Help remove invasive species at one of our volunteer events, held regularly throughout the summer months to pull Himalayan Balsam 
  • Form a community group to pull Himalayan balsam along a stretch of river


Our work on invasive non-native species is part of a county-wide collaborative effort to stem the introduction and spread of freshwater and riparian invasive non-native species (INNS) within Cumbria.

We work with many organisations to tackle INNS, including the Environment Agency, Natural England, the Lake District National Park, National Trust, Derwent Owners Association, the Borough and County Council and, perhaps most importantly, a significant number of volunteers who are passionate about their environment and work tirelessly to keep Himalayan balsam in check.

As with all our project work, INNS management is dependent on funding and we endeavour to incorporate INNS management into all our applications for funding. Where funding for this work is not available, we continue to keep a record of INNS identified while providing support and advice to our partners and the public.