Invasive non-native species (INNS)

Invasive, non-native species (INNS) are widespread across various habitats in the UK and our waterways are no exception.

Volunteers help us to survey invasive plants and record their spread and abundance along the Beverley Brook, Wandle and Hogsmill rivers. This information is then shared with partners and used to develop a plan of action to manage or eliminate these unwanted visitors.

  • River Rangers trained


  • Km of river surveyed for INNS


  • Volunteer hours managing INNS


What are INNS?

INNS (whether animal, plant or fungus) tend to have similar traits that make them successful, such as the ability to colonise areas rapidly, quick reproduction or propagation and a lack of natural predators.

They are a threat to our ecosystems as they often outcompete our native species for access to resources such as food, space and light. Some invasive species can have other negative impacts such as destabilising river banks and creating a public health risk.

Which INNS can you find on our rivers?

Common invasive plants on our rivers include Himalayan balsam, floating pennywort, New Zealand pigmyweed, giant hogweed and Japanese knotweed.

Invasive animals that you may see on London waterways include Chinese mitten crabs, signal crayfish and American mink.

A volunteer holding a signal crayfish © South East Rivers Trust

River Rangers

Volunteers are essential to our work to monitor and manage invasive plants on the Hogsmill, Wandle and Beverley Brook.

As part of our River Rangers initiative, volunteers are trained to correctly identify and record the abundance of key invasive plants. Our River Rangers survey the Wandle, Beverley Brook and Hogsmill annually, building up a picture of where the invasive species are and how well our management efforts are working in controlling them.

River Ranger surveying for invasive non-native species © South East Rivers Trust

From the source

Rivers can act as dispersal highways for invasive plants, helping seeds spread downstream. This is why it is important to coordinate efforts to eradicate invasive species from their source.

Through our Catchment Partnerships, we ensure coordinated and strategic control of INNS.  By sharing the results from our River Rangers partners, we can work together to create joined up strategies that increase the efficacy of INNS management.

Map showing non-native invasive species from source to Thames © South East Rivers Trust

The Hit Squad

INNS management involves a variety of species-specific approaches which are identified in the strategies developed through partnership working. Management may involve hand removal, cutting, spraying, trapping or biological control.

We run regular events throughout the summer to tackle Himalayan balsam and floating pennywort, both of which can be effectively managed by hand pulling. If you’d like to get involved and join our Hit Squad, you can sign up for our mailing list or keep an eye on our events page.

Himalayan Balsam removal © South East Rivers Trust

Thanks to our supporters

Catchment Based Approach
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Thames Water