Invasive non-native species (INNS) are defined as species that have spread outside of their natural range and threaten native biodiversity. The Colne catchment is blighted by a significant number of INNS associated with the aquatic environment such as Himalayan Balsam, Floating Pennywort, Signal Crayfish and even American Mink.

The impact of INNS both locally and nationally are vast. They are detrimental to the natural environment, which can lead to native species being outcompeted, such as for space or food, causing population declines and crashes. Declines of native species populations can have multiple negative impacts regarding the state of the local environment and ecology, which then reduces the provision of services these ecosystems provide. For instance, Himalayan Balsam is a highly invasive perennial plant that can cover the banks of rivers and outcompete local species in this habitat space. As well as reducing the diversity of plant species to support invertebrate populations, Himalayan Balsam dies back over the winter leaving infested banksides bare of vegetation. Lack of vegetation on banksides increases the rate of erosion, causing loss of land, such as that of farm owners.

Additionally, invasive species are proven to have negative economic and social impacts. For example, pennywort infestations can mean that angling and boating activities becomes impossible due to large mats covering the rivers. When these pennywort invasions become out of control and cover the river surface, this can drive increased risk of local flooding, increasing economic costs due to damage to infrastructure. Moreover, there are huge costs associated with control and removal nationally of INNS. These economic costs are also exemplified in the case of signal crayfish where there is a significant cost associated with the undermining and subsequent collapse of structures due to their burrowing activity.

Attempts to control invasive species throughout the Colne Catchment are carried out by several organisations such as the Chilterns Chalk Streams Project, Wildlife Trusts, Colne Valley Fisheries Consultative (CVFC), Community Connections CIC, River Chess Association, Angling clubs and Impress the Chess. Any actions to control the spread of an invasive species should be undertaken in a consistent, coordinated manner, ensuring that plans are in place to prevent their return. That is easier said than done of course – they are called ‘invasive’ for good reason!

ColneCAN has a working group focused on this issue which seeks to co-ordinate efforts and develop a catchment wide strategy. Volunteer groups have been essential for causing a significant reduction of multiple species in recent years. We are also working in partnership with Centre of Agriculture Bioscience International (CABI) who are delivering biological control for INNS throughout the catchment. The most exciting of these is the introduction of a weevil that feeds and breeds exclusively on Floating Pennywort.

INNS Mapper is a national INNS reporting system that can be used to record new invasive species that have been spotted in your area. Locally we also encourage the use of the INNS reporting site developed by CVFC. This allows those working within the Colne catchment to record INNS within the catchment, map their spread by adding to previous records, record management activity, and compare records year to year so we have an indication of the progress being made.

Some INNS can be spread very easily from site to site, for instance pennywort can regrow from a single lobe of plant matter. It is particularly important to be vigilant if you have been undertaking removal work but if you are an angler or even just taking a countryside stroll, please ensure that you comply with ‘Check Clean Dry’ protocols before leaving/entering a new site or area

We are currently looking for new volunteers to assist with invasive species monitoring and/or removal efforts! If you are interested, please contact our INNS co-ordinator Lara Clements at  This email address is being protected from spambots. You need JavaScript enabled to view it. or 07561706681.

More Information

An updated assessment of the direct costs of invasive non‑native species to the United Kingdom, Eschen et Al, June 2023, Centre of Agriculture Bioscience International (CABI)

Affinity Water, Colne Valley Fisheries Consultative and CABI combine to defeat Floating Pennywort

INNS reporting site developed by CVFC

Check Clean Dry Help stop the spread of invasive plants and animals in our waters! 

Design by LTD Design Consultants and build by Garganey Consulting. From an original concept by the Herts and Middlesex Wildlife Trust.