Thames Eel Project Workshop

Author: James White, RRC

On Tuesday (30th March), myself and Alex Bryden represented the RRC at the ‘Thames eel project workshop’ organised by Joe Pecorelli of the Zoological Society of London. The workshop was centred on a citizen science initiative, whereby volunteers will map instream infrastructure across the Thames region using the ‘River Obstacle’ app in order to help identify restoration options for eels. This project is the Thames Catchment Community Eels Project, led by Thames Rivers Trust. ZSL and TEP are collaborators on the project and the project partners are Action for the River Kennet, South East Rivers Trust and Thames21. The purpose of the workshop was to present initial steps taken for this project and gather feedback from various stakeholders and organisations (RRC, Environment Agency, Rivers Trust, Thames21) on how this can be delivered.

River fragmentation represents one of the primary pressures impacting river ecosystems globally. Yet, attempts to establish a ‘complete’ picture of all instream infrastructure are often undertaken across individual watercourses, and rarely at the catchment-scale necessary for river management strategies. While larger infrastructure like dams are often mapped and incorporated within freshwater management strategies, smaller infrastructure like weirs and culverts are more difficult to monitor. This presents a particular issue as smaller infrastructure may inflict threats to ecological health, and their uniquity across the landscape may result in them yielding greater cumulative impacts compared to larger infrastructure. As such, new methods for capturing the distribution of all forms of instream infrastructure are required to guide effective management strategies. Citizen science represents a potential strong route forward as it allows a large number of volunteers to collect reliable data, thus allowing measurements to be collected across large spatial areas.

For eels specifically, instream infrastructure represents a key issue for them completing their life-cycle strategy which includes significant longitudinal movements across river systems. After introductions led by Joe, Darryl Clifton-Dey (Environment Agency) gave a presentation highlighting the vulnerability of eels to instream infrastructure and outlined how eel populations have declined in the Thames region in recent decades. This was then followed by a discussion on conserving and restoring eel populations.

Slide credit: Darryl Clifton-Dey (Environment Agency)

Joe then provided a presentation outlining training and health and safety procedures to consider before allowing volunteers to collect information on instream infrastructure across the region. This was followed by a presentation given by Wanda Bodnar (University College London), who is helping to develop the River Obstacle app. Wanda outlined various features of the app, including how to note the obstacle type and height and add photographs of the barrier. In addition, Wanda outlined how the app has been developed to allow users to enter information specific to managing eel populations, including crawling media (e.g. algae, moss) which eels may use to help pass the barrier. Such information will be used within a ‘Eel Barrier Assessment Tool’ (EBAT – name still under revision), which quantifies the likelihood of the barrier being passable for eel migration based on the inputted data.

Slide credit: Wanda Bodnar (University College London)

The River Obstacle app is currently live in a trial form (see, while certain features will be reviewed and refined over time based on user feedback. Wanda outlined the developers of the app will look to develop draft guidance and training material by mid-May, where there will be a second workshop summarising initial feedback and findings, which will then govern its functionality prior to its final release later in the year.

Link to more project information.


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