October 2025
Thames Rivers Trust – Briefing: Our Position Statement, the European Eel.
The European eel is synonymous with the rivers in the Thames catchment. Eels have an immense natural and cultural heritage here, once common and yet now this species is listed as critically endangered. This iconic fish is a keystone species. However, numbers have dramatically diminished and on some rivers, are no longer present.
Our Vision is for a vibrant and healthy Thames River Basin; and the European eel is an essential part of this vision.
The European eel has been listed as critically endangered on the IUCN Red List2 since 2008 due to dramatic declines in abundance recorded across all stages of its life cycle and much of its natural range. For instance, monitoring of the upstream migration shows that recruitment of young eel into the River Thames and other European rivers is only at approximately 10 per cent of what it was prior to the 1980s.
The eel population in England has declined by 95% in the last 40 years. One of the principal threats to eels in freshwater are barriers to migration. Weirs, sluices and other manmade structures prevent eel from wriggling and swimming up our rivers and streams to disperse, grow and mature.
As a keystone species eel play a key role in the ecosystem of which it is part. A healthy river ecosystem is balanced, the European eel is a significant food source for other wildlife, particularly, otter, bitten, osprey and heron. Eels are crucial scavengers, feeding on and thus processing decaying matter and this keeps our rivers healthy.
TRT is uniquely positioned to bring distinct value for improving the future for the European eel. We bring together well-respected experts in eel conservation and those with local knowledge, river expertise and strong links to communities to deliver strategically informed, evidence led eel projects that align with the Environment Agency’s Thames Eel Action Plan (TEAP) the central guiding strategy for all conservation work in the region; whilst training, involving, educating and inspiring people of all ages.
To fulfil its complex lifecycle the European eel requires free fish passage up and down our rivers. It has different requirements at different stages. Eels will spend the majority of their lives in rivers before returning to the Sargasso Sea to spawn. Man has built many barriers in rivers that prevent eel from migrating and this can prevent them reaching suitable habitats, food sources or escaping from pollution. These barriers need to be identified and assessed on the ground specifically for eel passability.
Between 2020-2022 TRT led and built a partnership across the catchment to aid the long-term survival of the eel through the pilot project, Thames Catchment Community Eels Project.
Together we delivered more than any one organisation could deliver alone, scaling up, sharing knowledge and skillsets, developing and trialling a now successful citizen science methodology for eel barrier walkover surveys (ObstacEELS). Coming together a ‘train the trainer’ model was used to train Project Officers to train local volunteers and increase robust collection of up-to-date data on 5 key rivers in the Thames catchment. This was expertly validated and fed into the Thames Estuary Partnership Greater Thames Fish Migration Roadmap, to inform strategic ‘fish migration visions’ for barrier removal or modification, to bring the biggest wins for eels.
TRT is supportive and champions well executed citizen science, through this project and more widely ZSL train volunteer across Greater London to monitor eel traps to continue collecting nationally recognised eel migration data. Data on the number of young eels (elvers) can highlight the impact of barriers.
Evidenced by our pilot project there is a clear need to raise the profile of this unusual and important fish; and to connect communities with their rivers. Through the focus of the eel we can raise awareness of and a passion for eels, rivers and the whole river ecosystem. This benefits communities, eels and the wider natural blue space environment.
TRT is a strong advocate for eels, we will work together with our Key Partners, future project partners, with the Environment Agency, communities and funders to work towards our vision.
Currently (October 2025), TRT has just received initial support from The National Lottery Heritage Fund for our partnership project, the Thames Catchment Community Eels Project. This is building on our earlier pilot project of the same name.
This initial support is made possible thanks to National Lottery players, the project aims to address manmade barriers that prevent Critically Endangered European eel migrating up our rivers, carry out 3 types of citizen science surveying to collect important data on this keystone species fish and across the Thames the project will roll out extensive and innovative outdoor, hands-on river and eel community education and outreach. Read our recent Press Release to learn more about this exciting new project.
