Restoring Access for Fish and Wildlife

Overview

Healthy rivers are connected rivers. When water, wildlife and sediment can move freely, rivers are more resilient, support greater biodiversity, and are better equipped to tackle issues they may face. At the South East Rivers Trust, we work to remove barriers, restore natural processes, and reconnect rivers so fish and wildlife can thrive. 

Why access matters

Rivers are living systems. To a certain extent, all species rely on being able to move up and down rivers. They require specific habitats at different life stages, either as juveniles, adults or to spawn. Other species such as salmon, sea trout and eel need to be able to access rivers from the sea to complete their lifecycles. Across the UK, this natural movement is heavily disrupted. 

• Only around 1% of rivers in Great Britain are free from artificial barriers  

• There is on average one barrier every 1–1.5km of river  

• Barriers are one of the key reasons many rivers fail to reach good ecological status  

These barriers fragment rivers, turning flowing ecosystems into disconnected, often degraded sections. 

The impact of barriers

Structures such as weirs, dams and culverts were often built for historic uses like milling, water supply or navigation. Many are now obsolete, but their impact remains. 

They can: 

• Block fish migration, preventing access to spawning and feeding habitats  

• Increase flood risk 

• Degrade habitat, creating stillwater conditions which our riverine species are not well adapted to thrive in. They also reduce oxygen levels 

• Impact sediment movement, smothering gravel beds with fine sediment upstream and starving downstream habitats of vital gravels. This can reduce the natural armouring of the river bed, leading to increased incision of the channel and disconnection from the floodplain. 

• Increase predation risk, as fish are delayed or forced into exposed areas  

• Fragment habitats, breaking rivers into isolated sections and affecting fish, invertebrates, plants and mammals. This restricts how species move, feed and reproduce, often forcing them to survive in poorer conditions and leading to more fragile populations. They can also prevent recovery after pollution incidents, stopping species from returning upstream and sometimes resulting in a complete absence of wildlife above a barrier 

Even small barriers can have a big impact—causing delays, increasing energy use, and reducing survival rates for fish.  

What we do

We take an evidence-led approach to restoring access for fish and wildlife, working across catchments to reconnect rivers. 

Removing barriers

Where structures are no longer needed, removing them is always the most effective and preferred solution. This restores natural river flow, improves habitats, and reconnects ecosystems. 

Barrier removal has been shown to: 

• Increase fish populations and diversity 

• Allow rapid recolonisation of habitats 

• Improve overall river health  

Improving fish passage

Where removal isn’t possible, we design and install solutions such as: 

• Nature-like bypass channels 

• Easements and modifications to existing structures such as rock ramps or the use of baffles 

• Technical fish passes such as Lariniers and pool passes 

These help fish move upstream and downstream safely.

A catchment-wide approach 

Ideally, we aim to take a catchment scale approach to improving access, although in reality, with the pure number of weirs within each catchment and the complexities that often surround them, this is often an aspiration to strive towards.  

 We prioritise actions where they will have the greatest impact, working with partners, landowners and communities to: 

• Identify key barriers 

• Target solutions strategically 

• Look for the biggest wins and ‘bang for our buck’.  

The removal of any barrier is a win. So, we also take an opportunistic approach as the situations lend themselves. This means taking a long-term view to opening the river system.