Ellie's Weir...ed Blog

In this post our GIS whizz Ellie Spilsbury outlines some of the work we have been doing to identify ways to improve the sustainability of the fisheries in our rivers and hopefully aid the return of salmon for the first time since the Industrial Revolution.

Look closely and you will see hundreds of Minnows collecting at the bottom of this weir, unable to ascend. See the area in the water that looks dark brown; they are Minnows.

Visit each of the three sections for more detail:

A familiar Story

Data analysis with a Salmon Splash of professional opinion

(Tr)outcomes expected

A familar story

Once upon a time, our River Aire had the highest Salmon population of any Yorkshire river. Then came the Industrial Revolution, which saw the wool and fabric industry boom throughout Yorkshire. Mills were constructed accompanied by weirs to harness our river's energy. Although the mills are now closed and are becoming swanky new flats, the weirs often remain, isolating ecosystems that lie between them. Weirs disrupt the natural transport of sediment downstream, causing a build-up of silt and gravel behind the weir, which is detrimental to the habitat of spawning fish. Since 2011, one of the Aire River Trust’s goals has been to increase the connectivity of our river and its tributaries by removing or re-configuring weirs to allow fish passage. Following earlier work to install fish passes through and downstream of Leeds, significant steps towards this goal were made in 2022 with the successful construction of four fish passes as part of the DNAire project.

When we see water flowing over weirs, creating the sounds of waterfalls and visually pleasing white waters, it is easy to forget their man-made heritage and artificiality. It is hard to imagine seeing through the eyes of a migrating trout or salmon; every cell in its body instinctively directing it upstream to spawn, using both the stars and the earth's magnetic field for navigation and then facing an unpassable wall of Yorkshire-dressed stone. It is often not just the height of the weir that presents the issue but the combination of weir height and the shallow depth of the concrete sill below the weir. The height at which salmon and trout jump is directly affected by the relative depth of the water at the foot of the barrier and the “hydraulic jump,” which boosts their leap.

The Environment Agency (EA) has identified around four hundred river obstacles within the Aire Catchment. However, we believe there to be many more. For example, the EA recorded two barriers to fish passage on Pitty Beck, yet on our Bradford Becks Walkovers, we found 11. This pattern is most likely repeated on each beck.  Currently, tackling the removal of every weir in the catchment is unattainable. So, how did we prioritise them into a workable top twenty?

Data analysis with a Salmon splash of professional opinion

With help from The Rivers Trust, we are the first regional rivers trust to code an ArcGIS tool to accurately calculate the length of a river (including tributaries and forks) that would be opened and re-connected by the removal of every mapped weir in the Aire Catchment. Alongside this, we analysed ecological assessment data, invertebrate biodiversity, local community data (including deprivation), and weir visibility to the public. We assigned a score to each outcome and designed a weighted decision-making matrix that identified the weirs that scored the most highly. The data only tells us half the story, so we took our results to our expert team and discussed those weirs for which a solution in the short(ish) term might be feasible.

Once we had twenty feasible weirs, it was time to ground truth our ideas. The purpose of site visits is to add or, more often, diminish our confidence in the feasibility of the weir so that we only carry the most achievable sites to the next stage. We evaluated the weirs’ condition, site access, utility services or abstraction points, and landowner engagement by photographing and recording the area, our thoughts, and encounters.

The most surprising discovery for me was the actual size of a weir. After months of viewing photographs without visual perspective, weirs can appear to be half the scale of the real-life structure. Take a moment to analyse this photo: how tall do you believe it to be? See the very bottom of the blog for the upside-down answer.


We are fast approaching the end of the site visits and write-up stage. It is time to narrow our shortlist of twenty weirs down to four. So, it will be back around the table for our professionals to decide on the four “leak” proof projects to invest in. These four weirs will be subject to a comprehensive feasibility study and design process. I hope my next blog post will include more designs, machinery, hard hats and re-naturalised rivers.

River Worth Improvement Plan

Current projects

Weir today. Gone tomorrow?

A group of postgraduate students from the University of Leeds have been visiting the riverside in Keighley as part of their "Engaging the Modern City" module. They've been keen to find out more about the river and what residents want to know about it. In response, they've produced the leaflet below.

On the front we will use several modules to present the issues we have investigated and a module at the back to recommend areas of PR activity around Keighley and to summarise our fieldwork

Jingzhe Zeng

A central theme they have been particularly interested in is the old weirs. What was their purpose? What do people hope might happen to them? Should they remain?

There used to be dozens of mills that thrived on the River aire, but now these mills have mostly been transformed into heritage for other activities.

The concern, however, is that the weirs that provided power to these mills still remain as part of the river channel, and from an ecological standpoint, they block the passage of fish that want to swim upstream for food, breeding, or refuge.

The ideal solution would be to remove these structures to make the river more level, or to build fish passes. For more details, check out https://aireriverstrust.org.uk/fish-passes/.

Please feel free to share your thoughts in the comments. Do you support the removal of weirs? Why or why not?

Jingzhe Zeng
Two fish leap in a graphic that divides text

Reconnecting the river for wildlife

The Aire Rivers Trust has just completed it's Developing the Natural Aire project. Together with the Environment Agency, we have built fish passes to link 40km of the river to encourage the return of Atlantic salmon.

“It is fantastic to know that these fish passes in the upper River Aire are working as designed, and important fish species are rediscovering their key habitat

“As well as reopening rivers to fish migration and protecting ecologically important and endangered species like salmon and eel, fish passes are an amazing opportunity to reconnect river-resident species and the local community.

“Over the coming years, we look forward to seeing a growing proportion of trout, chub, barbel and salmon run spawning journeys higher up the river and a recovery in their populations.”

Thomas Somerville, Environment Agency's Developing the Natural Aire Project Manager 

You can read more about fish passes here.

How Fish Passes Work

As we come to the end of Developing the Natural Aire, SImon Watts explains why building fish passes matters.

All fish need to move to feed, breed and shelter. Even fish who spend their whole lives in the river can travel considerable distances looking for the ideal spot. Barbel have home ranges up to fifteen miles. Many freshwater fish migrate much, much further. For migratory species, like Atlantic salmon and the European eel, access to the sea is essential. The Industrial Revolution has left us with a fragmented river. Weirs built to harness the power of water for mills, factories and for navigation, block the way. Fish trapped in their sections are vulnerable to pollution or predation. And species like Atlantic salmon trying to return to our cleaner rivers cannot reach spawning ground in the shallow headwaters.

Why Do We Need Them

Whilst trout and Atlantic salmon can sometimes be seen leaping up waterfalls, weirs present a unique challenge. They are often long and steep. Their surface is smooth with little variation in the flow of water. The deep pools found at the base of waterfalls which fish can leap from are replaced by shallow aprons of concrete and stone. Many coarse fish species cannot jump obstacles.
The Aire Rivers Trust works with partners such as the Environment Agency and landowners to overcome these obstacles. The ideal solution is weir removal which restores natural river habitat (returning the artificial ponded section upstream back to a more natural system). But in some locations this proves impossible. Weirs form part of the urban fabric of our landscape. Some are valued for their heritage or for their amenity value. Buildings are built close to them and complicate their removal.

How Do They Work

Yorkshire Water explains why we need them and how fish passes work

Mid construction footage of the new fish pass at Kirkstall Abbey Weir as part of our Developing the Natural Aire project

An explanation of how an eel pass works from a Canal and Rivers Trust project similar to our Developing the Natural Aire

Where weirs cannot be removed, the solution is engineering. Records show rough fishways built in France during the 1600s. Here bundles of branches were used to create steps in steep channels to bypass obstructions. Engineered fish pass design has come a long way since the first one was patented in 1837 in New Brunswick, Canada. All designs seek to make weirs passable to fish. The majority of modern fish passes on the River Aire are Larinier Passes. Metal baffles in the base of them slow the flow over the weir that fish can swim or leap through.

The reconnection of 60km of habitat in the River Aire by the Developing the Natural Aire project will allow the return of Atlantic salmon, sea trout and other migratory fish. Monitoring conducted alongside the project has recorded a brown trout travelling from Armley Mills to Cross Flatts in Bingley (and most likely beyond) in a huge 80-kilometre journey to search for new areas to feed, breed and shelter in. This journey would have been impossible before Developing the Natural Aire as weirs like Kirkstall Abbey were completely impassible to fish.

Better Becks

River Worth Restoration

The State Of Our River

Reporting Pollution on the River Aire

This blog post was written in mid-October before the government's Environment Bill went before Parliament and the fantastic and widely publicised public debate that has followed it. Unfortunately, we have been delayed in publishing it or updating it due to staff sickness. We are still publishing as it contains (amongst other things) some really interesting maps and data about our catchment.

It's quite a long blog. If you want to find out how to make a difference you can skip to the end to find links to actions to take now.

How healthy is the Aire?

The start of October saw the release of the "State Of Our Rivers" report by the Rivers Trust (a national charity that campaigns on behalf of the Rivers Trust movement). It makes grim reading. England's rivers are failing and looking close to home this story rings true.

Make no mistake, our rivers are improving. We mustn’t let community memories of foam blowing off the river and down streets in Castleford or fish gasping for air below Baildon weir dominate conversations. The passing policeman who told one of the catchment’s river fly monitors “You won’t find anything alive in the River Worth,” was wrong. Our rivers are full of life. Pollution sensitive fish species like Atlantic salmon and grayling can once again be found near Leeds. With them, otters and kingfishers have returned, but our rivers are not good.

Heron on the Aire with Brown Trout

However only five of the 51 water bodies in our catchment have good ecological health.

The State Of Our Rivers" report identifies the key impacts on our rivers as agriculture; the water treatment sector; and the urban and transport sector a quarter. Pollution is not the only problem, though, as abstraction and habitat destruction also play their part in impoverishing our rivers.

Agriculture and the Upper Aire

After finishing tackling large amounts of Himalayan Balsam on Eller Beck, I recently took a walk downstream through Craven looking for other areas it had spread to. Walking downstream for about three kilometres I found almost none. Intriguingly, this isn't the good news story I hoped for. Instead, I found many banks with sparse vegetation, leaving them open to erosion by high flows. Grazing, often at uncontrolled locations where sheep and cattle can actually walk into our rivers, also places significant pressure on our waterways. We know that soil washed into our rivers pollutes our rivers, adding nutrients and smothering the gravels that fish need for spawning.

Within the Aire, much of this comes from livestock rather than arable farming. Work such as that undertaken by the Upper Aire Project is key to excluding livestock from our riverbanks and providing farmers with alternative water sources. For farmers to get on board it is critically important that the government makes it profitable to become involved in environmental schemes. We can only hope that pilot schemes for Defra's Environmental Land Management Schemes start to give the clarity farmers need for long term business planning.

Cows grazing beside the River Aire
Photo © Bill Harrison (cc-by-sa/2.0)

The Leeds Flood Alleviation Scheme Phase 2 is a unique opportunity for the Aire catchment. It echos a key theme of the State Of Our Rivers report that nature holds the key to us becoming climate-resilient. Renaturalising and remeandering channels; reconnecting floodplains; together with the creation of natural flood management features like tree planting, leaky dams and soil aeration hold the key to reducing the flood risk to our homes and communities. We are currently involved in a pilot project working with landowners to identify natural flood management potential. If you would like to know more please get in touch.

In the meantime, we will once again be planting trees this winter. Even with the disruptions of Covid, our staff and volunteers have planted over 5,500 in the past two years. There will be many more needed.

Planted trees

Get involved

You can help improve our local rivers by volunteering at one of our weekly volunteer sessions. the work we do ranges from planting trees to cleaning up the riverbank to laying hedges. Through this we hope to will introduce you to our fantastic river, others who care about it and offer you an enjoyable and rewarding experience.

We're particularly keen to recruit volunteers for our new citizen science project. The work they will do will help us understand our catchment, its health and the opportunities for improvement in it. You can find out more on our volunteering page.

If you spot pollution happening you can report it to the Environment Agency on 0800 807060.

Two leaves sit in a graphic that divides text

The impact of cities like Bradford and Leeds

The sewerage infrastructure that runs our streets was first put there by the Victorians and fundamentally, whilst populations have grown and the way we live has changed, those sewers are no longer up to the job. House building puts increasing strain on the sewerage network. To prevent sewage backing up into our homes, water companies are permitted to overspill untreated sewage into rivers during extreme rainfall events. However, these discharges happen with alarming regularity. The worst combined sewer overflow in our catchment is at Ingrow Lane in Keighley and discharged for a total of 2092 hours in 2020 (139 events of over 12 hours). You can explore your local area on the Rivers Trust's interactive sewerage map here. The blame for this doesn't rest solely with water companies and housebuilders. We buy new stuff and flush disposal cleaning products downpipes that were never built for them. Wet wipes form a depressing feature of every river clean up we do. We need the government to bring legislation that not only impacts water companies but manufacturers too. If you use wet wipes, please put them in the bin and NOT down the toilet.

At the launch of the State of Our Rivers report the Minister for the Environment Rebecca Pow boasted that, over the hill in Ilkley, her government has taken the step of designating the first river with the first inland bathing water status. This is a river I swim in regularly with my kids but she omitted to mention it is completely failing to meet the standards for this. (She also incorrectly named the swimming spot Otley which would no doubt horrify a few locals!) We all deserve rivers that are fit to play in whether it be fishing, swimming or canoeing.

Yorkshire Water has made some significant improvements over the past couple of years but our water bodies are still heavily impacted by both partially treated and untreated sewage discharges. Industry has played a huge role in the history of Airedale and we find a great deal of it remains along the banks of the Rivers Aire and Wharfe. We need to work with these industries to help them understand the risks they pose to the environment. Both Bradford and Leeds made the top five areas with serious water pollution incidents.

To tackle pollution in our rivers we need major investment in our sewage infrastructure. This is something that we not only need the government to demand but also to be willing as water consumers to pay for it.

Two leaves sit in a graphic that divides text

The change we need

All these problems need urgent action. Our rivers cannot wait for politicians and corporations to improve our environment little step by little step. They need bold leaps into action.

We need robust legislation to protect our waterways and an Environment Agency that is funded well enough to enforce them.

We need the funding in place that enables charitable partners, farmers, landowners and water companies to make the investments that create sustainable change. Some of this will come from the government but some must come from us recognising the value of our environment and accepting that we must fund it, for example through the prices we pay for food.

We also need to take local action - wet wipes and fat in the bin not down the drain, take your litter home with you (you might leave it on the land, which is bad enough, but much of it then gets blown or washed into our rivers, get a qualified plumber to put in your washing machine or dishwasher and make sure they connect to the sewer and not the surface water drains and come to volunteer your little bit "every little helps" (to steal ASDA's tag line!)

Two leaves sit in a graphic that divides text

Exploring our catchment

Only when people realise there is a problem are they likely to act. So we believe the best way to create this change is to share information. We need to connect communities to their river and each other to demand and bring about change. By making this data public we can hold regulators and polluters accountable.

As an example of the sort of information we hold and make freely available, the following map was created as part of a workshop to look for opportunities for improvement within Bradford Council's area. We want to use data to drive our decision making allowing us to make the most impact with our work.

This might seem a bit 'techy' but bear with us, it is simpler than it looks.

You will need to press the ">>" button in the top left hand corner to reveal the legend. Then click the tick boxes to add or remove layers of information from the map. Clicking the ">" button by each layer will reveal the full key.

An explanation of what each layer means can be found below.

Public Paths Outer / Bradford Public Paths / Other Paths Outer - Public footpaths in the Bradford area. Supplied by the Council as three layers but can be considered one dataset. This map was produced for a Bradford event so data has not been added for Craven or Leeds.

EA Risk of flood rivers Aire Clip - An Environment Agency assessment of flood risk/

Bradford Council Land - Land owned by Bradford Council

Cat1 2 Env Pollution Incident Aire Catch / Cat 3 Pollution Incident Waterbody heatmap - Water pollution incidents categorised from Category 1 (most serious) to Category 4 (least serious and not included in this map). Category 3 incidents are mapped as a heat map rather than individual incidents (as Category 1 and 2 are). You can read more on page 36 of this document here.

RiverObstaclesLayer Aire Catchment - Obstacles blocking fish passage in the river.

YorkshireWaterEDM2020 Clip - Yorkshire Water "Event Duration Monitoring" recording how long and how frequently combined sewer overflows released diluted sewage into water courses. You can read more here.

WB Aire Catchment WFD 2019 Fish 08OCT / WB Aire Catchment WFD 2019 Invertebrates 08OCT / WB Aire Catchment WFD 2019 Phosphate 08OCT / WB Aire Catchment WFD 2019 Ammonia 08OCT / WFD River Surface Water Aire Catchment only 2019 - The EU’s Water Framework Directive (WFD) which was adopted by the UK in 2000, imposes standards for the improvement of all aspects of water environments, including rivers, lakes, estuaries, coastal waters and groundwater. It requires surface water or ‘blue space’  to be of good quality by 2027. It assesses a number of chemicals and ecological components and rates them from High to Bad.

WB Aire Catchment WFD 2019 - Individual catchments are given assessments based on the lowest scoring component.

Aire Catchment River outlines - Our major watercourses.

OSMapWaterCourses Aire Clip - And minor ones.

Aire Catchment - The area covered by our catchment.

Two leaves sit in a graphic that divides text

A call to action

There are lots that you can do to make a difference. Why not join us as a volunteer on the riverbank or make small changes in your home, like installing a water butt? The Aire Rivers Trust doesn't work alone. Nearly every river has Rivers Trust and we have an umbrella organisation called "The Rivers Trust" that campaigns on our behalf. Head to their website to learn more about the issues facing our rivers and to help them by writing to your MP.

If, after looking at the map above, you have suggestions of projects for us to develop to improve the Aire catchment please get in touch with our Catchment Officer, Billy Coburn, by emailing him at billy.coburn@aireriverstrust.org.uk .

Two leaves sit in a graphic that divides text

The Electronic Aire

Brown trout after being tagged below Newlay weir

Lockdown. Restriction. Isolation. Are a few of the many words used to describe 2020. However, these words may also be used to refer to our river systems and the challenges faced by many of the fish populations that reside within them. Whilst many of us were house bound in 2020, construction of four fish passes to help reconnect habitats for river resident and migratory fish species in the River Aire commenced. Here I hope to give you all an insight into how I tagging fish by implanting electronic tags allows us to find out what is going on beneath the water surface, and what difference these fish passes are having on the lives of our fish.

The effect of weirs on wildlife

Barriers such as weirs and dams disrupt fish migration routes, fragment fish populations, and are a major contributing factor to the extinction of fish species globally. In 2020, a scientific paper (Belletti et al., 2020) highlighted how there are over 1 million barriers that fragment European rivers, with an estimated 48,293 barriers in UK waterways, each restricting or halting the movements of native fishes in some form.

The River Aire has 34 major weirs situated along its 114-km length that are barriers to resident and migratory fish. Fish passage solutions (fish passes) have been installed on many of these weirs to help improve movements of fish along the River Aire. The DNAire project is constructing fish passes on another four weirs (Armley, Newlay, Kirkstall & Saltaire), with the major aim of enabling upstream migrating adult Atlantic salmon to reach spawning grounds at Skipton.

These fish passes do not just open up migration routes for the iconic salmon, they will hopefully provide passage routes for river-resident coarse and salmonid fish species too.

How efficient are fish passes?

In conjunction with the DNAire project, the University of Hull International Fisheries Institute (HIFI) together with the Environment Agency are investigating the movements of fish in the Aire.

One of the key aims of this investigation is to assess the efficiency of the DNAire fish passes at Newlay and Saltaire weirs. To achieve this aim, HIFI have spent the last three years capturing and tagging fish (brown trout, barbel, roach and chub) between Armley and Hirst Mill. In addition, efforts are being made to capture and tag Atlantic salmon in the lower Aire that will hopefully migrate upstream and pass through the DNAire fish passes. Passive Integrated Transponder (PIT) tags, similar to those put in cats and dogs, enable us to identify individual tagged fish.

These tags do not have a battery – and thus last the life of the fish – and emit a unique ID when activated by an electromagnetic antennas installed inside the fish passes. The antennas are strategically located to detect when fish approach, enter and ascend each fish pass. With this data, we can calculate the fish pass performance as well as provide additional information on environmental conditions when particular species move through the catchment.

Saltaire fish pass during construction. The baffles in the Larinier fish pass (left) can be seen with PIT antennas mounted on wooden beams across them. The plastic eel pass can also be seen (right).

Building knowledge for the future

Investigating fish pass performance and factors influencing passage is key to understanding effectiveness of fish passes constructed during the DNAire project and for developing future fish passes. We are all working towards a more natural and healthy River Aire that both fish and society can benefit from. We will continue to collect data in the coming months and will hopefully share results with you in a future blog.