29. Floating Pennywort Control in the Colne Catchment

Aims: Control invasive non-native species; Involve people with their local waterbodies; Improve wildlife corridors; Improve water quality; Manage flow; Work together

Water body: River Colne

Project description

This project proposes to tackle the problem of the non native invasive species Floating Pennywort that has successfully infested the Colne Catchment through a) biological control delivered by CABI and b) physical removal & community engagement.

Floating Pennywort is an Invasive Non Native Species that has a phenomenal growth rate – particularly in nutrient rich watercourses (20cm a day in peak summer conditions), it can suffocate watercourses to the detriment of wildlife and people.

Floating Pennywort covers large areas of the River Colne and its tributaries and is spreading, causing serious concern to angling clubs, conservationists and local communities.

For more information, see Floating Pennywort Public Leaflet

Biological Control

Due to previous work of Colne Valley Fisheries Consultative, Environment Agency, Groundwork South and others the Colne has been selected as a trial location to establish a Weevil from South America (Pennywort’s native area) that feeds exclusively on Floating Pennywort. Biological control has the added advantage that it can get to Pennywort in parts other control methods can’t reach  - such as amongst fallen trees or branches in the water.   After extensive research and trials a licence has been obtained from DEFRA to release the Weevil in the Colne, one of only three pilot areas in the UK. It takes approximately 5 years to successfully establish a self sustaining population in the wild to acclimatize and adapt to the habitat and build up some resilience.  The first five years is an investment for all those years that follow. We are currently in year 2, this project will focus on years 3-5 starting in April 2023. 

Physical Removal & Community Engagement

This will take place involving local communities in physical control to keep on top of the infestation in the areas away from the Weevil release sites.  We will undertake at least 30 work sessions/year at a variety of sites across the northern part of the Colne Valley Regional Park from Rickmansworth to Denham/Uxbridge focusing on the River Colne and its side channels and the River Misbourne downstream of Chalfont St Peter. Physical removal will be away from Weevil release areas because we don’t want weevils being removed with the Pennywort.  Volunteers will be trained to carry out monitoring so that they can recognise Weevil presence as their range and distribution grows.

Outputs over 3 years

Support for the CABI research programme to ensure a successful viable population of Weevils. The research outputs will include further understanding of the success of the Weevil as a biological control in the UK. This will provide a case study that could lead to a long term UK wide solution for Floating Pennywort, a damaging and costly invasive species.

At least 100 Pennywort control volunteering sessions involving at least 5,000 person hours. Community engagement via articles in local publications and social media and conversations (‘door knocking’) with riparian landowners to educate and encourage positive action.

Over 10km of watercourse directly improved for biodiversity. Leading to natural control in perpetuity across the Colne Catchment which includes 100’s of km of watercourse.

The Case for investment

The environmental case - An invasive non native species which excludes naturally occurring native species and negatively impacts on the water environment – physically (shading and occupying space, chemically pH) and shading impacts/temp control. Detrimental to the watercourse and the Water Framework Directive.

The community case -  impact on angling and the visual appearance/amenity value of rivers.  There is high public concern and many offers to help. These offers need support and guidance including to stop well-meaning actions inadvertently causing more problems eg letting Pennywort float downstream, putting it in council green waste bins or removing beneficial species such as Watercress.

The business case. Impact on fisheries, navigation & other commercial interests. However, the key business case for investment in this project is the fact that a Biological Control agent is now available, which can provide a cost effective means of removal given the size and scale of the task. 

We have launched and Appeal to help fund this project: Donate here to help local rivers flow freely again. Thank you.

Project lead: Groundwork South

Project partners: Environment Agency, Colne Valley Fisheries Consultative

Contact for more information: This email address is being protected from spambots. You need JavaScript enabled to view it.

Project start: April 2023

Project end: 2026