A Surprise Encounter on the River Stour: Fish Surveys, Elvers and Partnership Working

Sometimes the best opportunities happen when you least expect them!

This month, while carrying out Himalayan balsam removal on the River Stour between Stratford St Mary and Langham, the Essex and Suffolk Rivers Trust team had the chance to join colleagues from the Environment Agency during one of their routine fish surveys. What started as a day of 'balsam bashing' quickly turned into an opportunity to learn more about the health of the river and play a small part in supporting one of the UK's most remarkable native species.

Monitoring the health of our rivers

The Environment Agency carries out regular fish surveys on rivers across England to better understand the health of our freshwater environments. Fish are excellent indicators of river condition because different species have different habitat requirements and varying tolerances to pollution and environmental change.

Pike (Esox lucius)

Perch (Perca fluviatilis)

Pike (Esox lucius)

Using specialist electrofishing equipment survey teams can temporarily stun fish so they can be safely identified, counted, measured and recorded before being returned unharmed to the river. The information collected helps build a picture of fish populations over time, allowing the Environment Agency to monitor trends, identify pressures on rivers and assess whether restoration work is having a positive impact.

These surveys also provide valuable evidence to guide future river management and conservation projects.

A special opportunity to release elvers

Following the survey, our team was invited to help release a bucket of elvers (baby eels) into one of the farm's ponds. It was a memorable experience and a real privilege to contribute to the conservation of this fascinating species.

Two people crouched near the edge of a pond tipping a blue bucket full of small eels into the water

The ponds provide an ideal refuge for young eels. Although they are currently isolated from the main river, adult eels are able to slither across approximately 10 metres of damp grass to reach the River Stour and continue their remarkable migration. However, young eels cannot naturally reach the site because the weir at Judas Gap, near Flatford, currently prevents them from moving upstream.

Elvers are juvenile European eels (Anguilla anguilla), often referred to as 'glass eels' because they are almost transparent when they first arrive in our rivers from the sea. Their journey is one of the most extraordinary migrations in the natural world.

European eels begin life thousands of miles away in the Sargasso Sea in the western Atlantic Ocean. After hatching, they drift on ocean currents for up to two years before reaching the coasts of Europe. As they enter estuaries and freshwater rivers, they develop into elvers and begin migrating upstream, where they can spend anywhere between 5 and 20 years growing before making the incredible return journey back to the Sargasso Sea to breed.

Unfortunately, European eel populations have declined dramatically over the last few decades due to a combination of habitat loss, barriers to migration, pollution, changes in ocean currents and illegal fishing. The species is now listed as Critically Endangered on the IUCN Red List, making conservation efforts more important than ever.

Releasing elvers into suitable habitats gives young eels the opportunity to grow and thrive, helping to support local populations and contributing to wider conservation efforts for this iconic species.

Working together for healthier rivers

Our unexpected encounter with the Environment Agency was a brilliant reminder of the value of partnership working. Whether we're removing invasive non-native species such as Himalayan balsam, monitoring river health or helping to restore threatened wildlife, collaboration is essential to achieving healthier rivers for people and nature.

By sharing knowledge, expertise and opportunities, organisations like the Essex and Suffolk Rivers Trust and the Environment Agency can have an even greater impact than working alone.

We'd like to thank the Environment Agency team for welcoming us onto the survey and giving us the opportunity to take part in the elver release. Experiences like this strengthen our partnership and reinforce the shared commitment we have to restoring, protecting and enhancing the rivers of Essex and Suffolk.

Find out more

• Learn more about our Himalayan Balsam control

• Explore our current projects