We have looked at how barriers harm fish, blocking migrations, degrading water quality and fragmenting habitats that once stretched uninterrupted from source to sea. But these structures didn’t appear from nowhere. Britain’s rivers have been put to work for millennia, and many of the barriers we are dealing with today are the legacy of industries and ways of life that have long since changed or disappeared entirely.
So why were they built? Our campaigns researcher, Danny Nixon, explores this and asks: Which ones do we still genuinely need?
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River barriers are not a modern invention. The oldest known dam was built around 3000 BC at the Bronze Age settlement of Jawa in Jordan. In Britain, our rivers have been dammed, diverted and controlled for thousands of years.
But it was the Industrial Revolution that transformed the scale of barrier construction beyond recognition. Britain’s rivers became the engine of the world’s first industrial economy, powering mills, supplying canals, feeding reservoirs and providing the water infrastructure on which expanding cities depended. From the Pennines to South Wales, and from Lancashire to the Midlands, the rivers that ran through our industrial heartlands were put to work in ways that required extensive physical modification.
Man-made barrier density is highest in historically industrialised areas, including Greater Manchester, the Midlands, South Wales, and West Yorkshire. The Mersey catchment alone contains nearly 2,900 man-made barriers, a density of 1.14 per square kilometre. In parts of South Wales, that figure rises even higher.
Before talking about which barriers should be removed, it’s important to be realistic about the structures we still depend on. The case for barrier removal is not a case against all river infrastructure. It’s about being smarter and more targeted when deciding which structures are genuinely necessary.
Some barriers remain essential to modern life in the UK. Here’s why:
In many cases, the same structure serves multiple purposes simultaneously, making removal complicated. A weir that is technically ‘redundant’ in industrial terms may still influence flood management downstream, or may have become part of a local ecosystem in ways that complicate simple removal.
That said, reconnecting our rivers is essential to the future of wild fish – particularly migratory species whose life cycle depends on connected waters.
A significant proportion of barriers in our rivers serve no meaningful purpose today.
It is estimated that around 150,000 of Europe’s approximately 1.2 million recorded barriers are now obsolete, no longer fulfilling their original purpose (Dam Removal Europe, 2022).
In the UK, some datasets have suggested up to 20% of recorded barriers are no longer in active use (Rivers Trust, 2025). The true figure may be higher, as information on barrier usefulness is poorly recorded. In most UK barrier datasets, this field was left blank or marked unknown for the vast majority of structures.
WildFish’s analysis has shown that the most common barrier types in the UK are not large dams but culverts (62% of all artificial barriers) and weirs (28%). Many of these are small, old, and connected to industries that ceased operating decades ago. Former mill weirs on rivers across the Pennines, old industrial culverts beneath urban streets, and agricultural diversions from a different era of farming. Thousands of these structures are now sitting in our rivers, blocking fish and trapping sediment, with no one who relies on them and no reason for them to stay.
There’s also a practical financial argument for removal. Many of Britain’s concrete dams and weirs were built in the early twentieth century with design lives of around 100 years. They are now approaching or past that lifespan, and ageing infrastructure requires regular, costly inspection and maintenance. In many cases, removing a structure entirely is cheaper in the long run than keeping it in place, and delivers ecological benefits that maintenance never could.
Across Europe, there is growing momentum behind barrier removal as a mainstream river restoration tool. In 2023 alone, 487 barriers were removed across 15 European countries — a 50% increase on the previous year. France removed 156, Spain 95, Sweden 91, Denmark 72 (DRE, 2024). The UK removed just 36.
The EU’s 2030 Biodiversity Strategy has set a target of making at least 25,000 km of rivers free-flowing again by 2030, primarily by removing obsolete barriers. Good progress has been made; in 2024, over 2,900 km of river connectivity was restored.
But the UK, no longer bound by EU targets following Brexit, has no equivalent strategic plan. The UK’s National Biodiversity Strategy and Action Plan contains no specific mention of river barriers and no target for restoring river connectivity.
This is a significant gap. Without a national strategy that identifies priority barriers, allocates dedicated funding and sets measurable targets, barrier removal in the UK will remain patchy and slow. Instead, it will be driven by the efforts of individual river trusts and conservation organisations rather than the coordinated, catchment-scale action the problem demands.
Not all barrier removal is equal. The most effective approach targets the structures where removal will deliver the greatest ecological benefit.
One key concept is ‘passability’ – the percentage of fish that can successfully navigate past a given obstacle (Buddendorf et al., 2019). Passability depends on the type and height of the barrier, the target species, the flow conditions and, critically, the position of the barrier relative to others in the river. A single impassable barrier near the sea can cut off the entire upstream habitat from the marine environment. Removing it may unlock far more river than removing ten barriers higher up the catchment.
Research on the Tagus River in Spain found that removing just seven of twenty-nine barriers, identified through habitat modelling, could improve river connectivity by as much as 37% (Branco et al., 2014).
The message is clear: strategic and targeted removal delivers far more than random or opportunistic action – highlighting the need for a clear strategy in the UK.
When barriers do come down, rivers respond and fish return. Complete, large-scale removal is not always possible. Smaller-scale efforts can still have a positive impact, including:
1. Fish passage solutions
When trying to reconnect river habitats, complete removal of all barriers may not be possible, but removing just some obstructions and installing fish passage solutions can still have a great effect.
On the River Deerness (a tributary of the River Wear) in Northeast England, three barriers were removed, five barriers fitted with fish passes, and two barriers left unaltered between 2013 and 2019. Total fish abundance, comprising seven native species, increased three years after the restoration project and remained elevated to the end of the study (Sun et al., 2022).
An increase in habitat connectivity reduced the mean age of brown trout, suggesting a change to an increased migratory component of the population, showing the benefits barrier removal brings to resident fish species as well as migratory ones. Immediate geomorphic benefits observed included large increases in riffle habitats essential for salmonid spawning and decreased fine sediment loads. The study highlighted the immediate ecological benefits of connectivity restoration, especially in rivers with many barriers, but larger scale changes may take several years to develop.
2. Small-scale removal
Barrier removal does not have to be a large, expensive project to provide real ecological benefits. The majority of UK barriers are small obstructions, such as culverts, sluice gates and fords, many of which can be removed at low costs with simple solutions.
At Staindale Beck, in North Yorkshire, a concrete sleeper ford, installed over 30 years ago, was likely impassable to the majority of fish in the majority of flow conditions and was no longer in use by the landowner (Forestry England) after the installation of a bridge. The ford negatively impacted geomorphological conditions within the beck, with the channel impounded 25m upstream, creating a large area of unnaturally deep and slow-moving water and increased fine sediment deposition. Whilst the planning by Yorkshire Wildlife Trust took approximately four months to complete, the actual removal work carried out by a local contractor with an excavator took only one hour at the cost of £385!
These are not isolated success stories. They reflect what a growing body of international evidence consistently shows: barrier removal works, and it works faster than almost any other river restoration intervention. Fish respond quickly, and habitats recover. The ecological return on investment is high.
Take the Morton Quarry Weir in Linhouse Water, West Lothian. The two-metre structure, dating from the 1800s oil shale industry, was removed by the Forth Rivers Trust in 2023 (Mouchlianitis, 2024). The result was 8.5 kilometres of spawning habitat unlocked for wild fish upstream. Trout and salmon were observed attempting to migrate upriver even while the removal was still underway!
In the UK, we have more than 70,000 recorded barriers, and possibly well over 100,000 in reality. Most of these barriers are man-made, and a significant proportion of them no longer serve any purpose. Meanwhile, four of our seven most endangered freshwater fish species are in decline partly because of those barriers. This is no surprise when far less than 1% have any fish passage provision.
We want to see:
Our rivers were once among the most productive salmon and eel rivers in Europe. That can be true again, but we need to address the main threats. Reducing habitat fragmentation by removing obsolete barriers and reconnecting our rivers is key and should be considered alongside reducing pollution and abstraction in a holistic approach to river conservation.
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