The UK's rivers are riddled with sewage pollution – new wetlands could help clean them up

As effluent from sewage works and agricultural pollution flow freely into rivers, researchers and local citizens are urgently seeking to clean up the UK's waterways. New wildlife-rich wetlands could be an answer.

The Norfolk Broads in the east of England are famed for their rivers and lakes, rare chalk streams and wildlife. But it had been clear for some years to local people that some of the waterways were anything but pristine.

Just a few miles inland from the rolling sand dunes of Norfolk's coastline and the picturesque seaside town of Cromer, vegetation and wildlife in the upper River Mun were suffering. In the lake called the Little Broad, into which its waters flowed, fish were dying.

The cause, it turned out, was sewage pollution. The dumping of raw sewage in waterways is a widespread problem across the UK. The amount of raw sewage spilling into England's rivers and seas doubled in 2023, with 3.6 million hours of spills compared with 1.75 million hours the year before, according to the UK's Environment Agency.

But, in the case of River Mun (also known as Mundesley Beck), the problem wasn't illegal dumping or excessive overflow – the discharge from the nearby sewage treatment works at Northrepps was treated and completely legal. The problem is that treated "effluent" may still be harmful to the ecosystems it flows into, according to many river experts.

This exemplifies just how complex the UK's sewage pollution problem is. Around the country, local groups are taking matters into their own hands as national systems struggle to keep up with growing pressures on the country's sewerage infrastructure. The state of the River Mun and Little Broad spurred a local conservation charity, the Norfolk Rivers Trust, to look for a solution. After drawing on models from around the world, they decided to create their own natural fix – they built their own wetlands to act as a natural filter.

Local solutions such as this can be very effective in improving river health, according to Dania Albini, who researches freshwater pollution at the University of Exeter in the UK. Other community-based solutions which can be done by local volunteers include patrolling waterways for problematic sewage outflows or monitoring water quality using established wildlife-based methods.

The country's rivers are far from healthy – one of the environmental issues that was at the forefront of the UK's general election.

Just 14% of England's rivers meet the standards of a "good ecological status" under the Water Framework Directive for England and Wales.

The most ambitious target under the directive was to have all rivers meeting this standard by 2015, says Mark Lloyd, chief executive of The Rivers Trust, the umbrella organisation for river trusts across the UK and Ireland. The goal then became to get 75% of rivers to this standard by 2027, he says, adding "we haven't a snowball's chance in hell of reaching that".

Agriculture and land management have the greatest impact on river pollution, but sewage pollution is also a major part of the problem, Lloyd notes. "Sewage is a big one. There's been a lot of focus on stormwater overflows – when untreated sewage gets discharged into rivers, which obviously is awful, but it's not in ecological terms the biggest factor."

Sewage pollution can upset aquatic ecosystems, harming wildlife and threatening human health as the pathogens it spreads in the water can cause infections.

While raw sewage is a problem, one of the most significant environmental impacts from sewage is from treated effluent, because it is often only partially treated, says Lloyd. At sewage treatment works, human wastewater typically goes through three stages. Firstly, solids settle out of the water in tanks. A second stage involves a biological treatment with bacteria breaking down pollutants in the water, much improving its quality. But a third stage, such as sand filtration, is optional. This is where "nature-based solutions" such as building new wetlands or "integrated, constructed wetlands" (ICWs) can come in, says Lloyd.

Wetlands are a "very effective way to fine-tune the water before it goes into a river," says Tanja Radu, an environmental engineer at Loughborough University in the UK whose research interests include wastewater treatment.

ICWs are particularly good in reducing the proportion of phosphates in wastewater, which come from human waste, soaps and detergents, says Lloyd.

"The problem is [phosphate is] a nutrient, so basically it's like putting extra fertiliser into streams," says Jonah Tosney, a river ecologist and technical director at the Norfolk Rivers Trust.

Phosphates from sewage (along with nitrates) can cause some vegetation to thrive at the expense of others, leading to algal blooms which blanket the water surface, blocking sunlight and causing eutrophication, whereby plants die and the microbes that decompose them use up the oxygen in the water, suffocating fish and other life. (Read more about the pollution causing harmful algal blooms here).

"It unbalances the ecosystem," says Tosney – a particular problem in the delicate ecosystems of the rare chalk rivers in his area.

Human contact with contaminated water can also cause illness due to harmful microorganisms, including parasites, says Albini. In fact, sewage pollution might be worse than agriculture for river health in terms of affecting water quality and the riverine community, according to research carried out by Albini and researchers at the University of Oxford in 2023.

In Norfolk, the building of new wetlands aimed to reduce the phosphate levels. The problems in the River Mun and Little Broad had been building for decades, says Tosney, so in 2014 Norfolk Rivers Trust built the Frogshall Wetland over a disused farm site and horse paddock using UK Environment Agency funding.

Instead of discharging straight into the river, a pipe from the treatment works led treated water into a series of three shallow ponds filled with native vegetation. The idea was that the excess nutrients would be absorbed away as the water slowly percolated through, finally flowing out into the River Mun.

"We saw the change in the stream pretty much immediately," says Tosney. "The really hungry vegetation that was really benefiting from the extra nutrients – that faded out within the first year. We saw improvements in invertebrate life in the first year. It was pretty dramatic really."

Monitoring in 2024 showed a 70-90% removal of phosphate and ammonia by the wetland, says Tosney. The group sampled concentrations as the water entered the wetland from the sewage works and at the outlet from the wetland to the stream. Biodiversity had also increased, with 10 bird species seen at the site in 2014 before the wetlands were installed, and 26 afterwards in 2016. The number of endangered bird species (using the British Trust for Ornithology categories) also increased from zero to four in two years, according to a 2020 study.

The project was so successful that the trust attracted the support of their local water company, Anglian Water, as well as other agencies, and has since built three more wetlands next to sewage works. Frogshall and Ingoldisthorpe wetlands (built in 2018) have been visited by multiple English water companies, with many carrying out feasibility studies. At least two – Wessex and Yorkshire Water – are building similar wetlands, says Tosney.

Ingoldisthorpe Wetland improved the water quality of the River Ingol from "bad" under the Water Framework Directive classification, to "moderate" in the two years after it was built. In 2023, wetlands were built at Langham and Stiffkey on the River Stiffkey. Tosney says the trust hopes to put a wetland next to the four other sewage works on the river.

A spokeswoman for Anglian Water says the work with the Norfolk Rivers Trust on these wetlands is a great example of “how partnership working can make a real difference” to environmental quality. "We want to work with others, such as farmers, local authorities and environmental organisations to solve river health problems together.” 

She adds: "We're already building treatment wetlands around the region and have plans for even more in the future, as well as other nature-based solutions."

Wetlands can be useful in tackling sewage pollution even in urban settings. In Enfield in London, Enfield Council and waterways charity Thames21 have worked with community volunteers to improve the overall health of rivers by restoring watercourses and creating wetlands for pipes from the urban drainage system to flow into.

"We see huge improvements in water quality downstream of wetlands," says Sam Bentley-Toon, the engagement manager at Thames21. "Water flows in full of phosphates from detergents and ammonia from human waste and it flows out clean."

At Firs Farm Wetlands, for example, the water that flows in is categorised as “poor” for phosphate and ammonia according to the Water Framework Directive, says Bentley-Toon, but the water that flows out scores “moderate” for phosphate and “very good” for ammonia."

Thames21 has also worked with volunteers to identify “misconnections” which lead to sewage outfalls where untreated wastewater is discharged into waterways. Some areas have separate sewer systems for surface water and wastewater, and sometimes waste pipes from households will mistakenly be plumbed into the surface water system, so waste will bypass treatment works.

A lot of problems with sewage in the UK may also be down to its antiquated system, says Lloyd. Much of the country's sewer system has grown organically over centuries, with surface water and human waste flowing into the same pipes that discharge into rivers. The problem with this "combined" system is that it vulnerable to the volume of water flowing into it, Lloyd says. When there is heavy rain, for example, this can exceed capacity and sewage ends up being discharged untreated into rivers.

Lloyd says the pressures on the overall sewage system are growing in three particular ways. Firstly, population growth means more sewage. Secondly, we are building over more areas: paving over gardens and building more infrastructure. And thirdly climate change means we are having more heavy and intense rainfall.

"But we've also not invested as we should have done in increasing the size of the sewage system, fixing leaky sewers…increasing the capacity of treatment works so that they can cope with sewage better and treat it to a higher standard," Lloyd says.

The Rivers Trust published its comprehensive 2024 report on The State of Our Rivers earlier this year, showing none of England's rivers are in good health. But the issue of sewage pollution "hotspots" is complicated says Lloyd, for historical and geographical reasons.

Most rain tends to fall in the north and west, so the sewerage system can be overwhelmed in the big industrial cities of the north-west such as Manchester and Liverpool.

"London has the same problem. It's a very large city with a Victorian sewer system," he says. However, the £4.5bn ($5.7bn) Thames Tideway "super sewer" currently being built should "largely stop most of the discharges of raw sewage into the Thames", he says. The super sewer is part of a Thames Water upgrade, London 2100, to the city's sewerage system.

Monitoring and flagging up problematic sewage overflows and misconnections to the relevant authorities is another way that local projects are improving river health. In the Bradford area, about 70 volunteers mapped sewage outflows along the River Aire and its tributaries for the Aire Rivers Trust last winter as part of a method called Outfall Safari, developed by the Zoological Society of London and other organisations. They walked the length of the waterways looking for pipes and used a smartphone app to score them on "aesthetic value", says Sam Riley-Gunn, citizen science project officer at the Trust.

"Basically, how gross did it look? Did it have sewage fungus? Did it have wet wipes? Did it have clear signs that there was bad stuff coming out of the pipe? And how far down the river that pipe was having an effect."

So-called "sewage fungus" is actually a mass of bacterial colonies that grow in nutrient-rich water and can reduce oxygen levels, and is associated with sewage entering waters. Wet wipes, meanwhile, are increasingly flushed into the system from households, adding to problems such as the massive, fatty blockages called "fatbergs" which block sewers.

This information is shared by the Trust in a map with the public, and with Yorkshire Water River Health team, who then report it to the Environment Agency pollution hotline to try and get enforcement. The work is yielding a wealth of information: the last survey covered 660 outfalls and identified discharges that should not have been happening including 22 high-risk and 39 medium-risk outfalls.

Defra and the UK's Environment Agency were unable to comment during the election period, but the agency flagged up its background guidance: "The EA values the contribution of England's citizen scientists and shares their passion for the environment. It welcomes various emerging initiatives that complements its own monitoring and assessment work and enables a greater level of engagement with partners."

The Aire Rivers Trust also works with community groups using another scientific initiative called Riverfly which looks at the mix of invertebrate species to assess river health, with the data going into a national database.

"The Riverfly project is particularly valuable, as it assesses river health by tracking sensitive macroinvertebrate populations, indicating the impact of pollution," says Albini.

In Bradford, Riverfly has identified serious issues, resulting in a prosecution against Yorkshire Water by the Environment Agency for a large pollution incident that occurred in Bradford Beck in 2018. A Yorkshire Water spokesperson told BBC Future Planet: "We have made significant improvements in our operations since this incident in 2018. We're committed to improving the health of Bradford Beck and work closely with Aire Rivers Trust and Friends of Bradford Beck to reduce pollution, including sources not related to Yorkshire Water assets, entering the beck via pollution reporting technology."

Riley-Gunn stresses that "what we have to do with the water companies is work with them to help them pinpoint the worst problems and to help them direct what funds there are to fix the worst bits first".

Radu says that while raising awareness among citizens is important, volunteers should not be expected "to be the police" in such situations. "The water companies need to do their part of the job," she says. "It's not only about monitoring problematic sewage spills, it's about avoiding it in the first place."

Ofwat, the economic regulator for the water sector in England and Wales, was unable to comment during the election period.

Radu notes that the government has met its target to fit event duration monitoring devices – which record the location and duration of spills – on storm overflow pipes for combined sewer overflows (CSOs). Companies are legally allowed to discharge some sewage from CSOs during extreme rainy weather.

However, she highlights a recent BBC investigation which found that raw sewage was being discharged during dry weather, meaning the pollution is more concentrated. "If you are super-concentrating sewage in rivers, that creates a whole new level for aquatic organisms to cope with,” she says.

In the longer-term, reducing the "peak" of water during rains may help cut sewage pollution. Lloyd talks about "sponge cities" with sustainable drainage systems and "soak away areas" designed to help water percolate slowly into the ground, so it doesn't all hit the system at once. (Read more about the spongy cities of the future in this article by Kate Evans.)

Lloyd says a "holistic approach" is needed to manage water in the landscape. "It's a really precious resource but we have far too much of it in the winter and we get lots of floods, and then we have droughts in the summer and we're desperate for it and supplies are really under threat," he says.

Multiple sources of funding and "action by everyone" is needed to manage water, he says. And while local projects can make a huge impact, more needs to be done at higher levels. "The overall the health of our rivers is flatlining at a low level, we have some of the unhealthiest rivers in Europe; and our wildlife is disappearing very rapidly," he says.

In the absence of such coordinated action and funding, community-led projects are making progress in keeping their waterways clean. Back on the River Mun in Norfolk the wildlife is slowly recovering, according to Tosney. "The algal blooms are less severe and the plant life is returning." And with their constructed wetlands, there are other gains too for bringing the community together and restoring habitat, he says. "They are absolutely brilliant for insect life, birds, water voles… We get a huge amount of life."

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