Episode 1: How Healthy is the Thames?

0:03At Blackfriars Bridge, right in the heart of London, boats are moving swiftly along the Thames, cutting through the current. To one side, the city rises up. Glass towers, cranes. And in the other direction, the Houses of Parliament, where, for decades, politicians have argued over the state of the river their offices overlooks. look. Beneath the pavement is something most people will never see. The Tideway Tunnel, a 16-mile super sewer whose construction spanned almost a decade. Designed to stop millions of tons of sewage from spilling into the Thames, critics argue it's a£5 billion plaster on a gaping wound.

0:54The super sewer is a marvel of engineering, but campaigners argue it's an expensive fix for a system that was hollowed out by its owners while the regulators looked the other way. Because for all the river's history and importance, the Thames has a problem.

1:23The water flowing past me right now began as a spring in the Cotswolds, more than 100 miles away. By the time it reaches central London, it's passed through farmland, towns, treatment works, and a system that, at times, still can't cope with London's growing volume of sewage. So the simple question at the heart of our series is, how healthy is the Thames today?

1:55Lucy Tobin: This is Thames Unfiltered from The Standard in association with Thames Water. I'm your host, Lucy Tobin, business journalist for The Standard, The Times and The Daily Mail and author of seven books. Across these six episodes, we're exploring one river and everything that depends on it. The Thames isn't just the wiggling division of North and South London. it's shaped by millions of people, managed by powerful institutions and relied on every single day. We'll hear from campaigners, scientists, politicians as well as the company accused of failing to look after London's river, Thames Water. Who's responsible when things go wrong?

2:41Lucy Tobin: Why is sewage still being discharged into London's river? And what needs to change to protect it in the future? In Westminster, the blame game has already begun. At Coombe in my constituency, Thames Water has pumped sewage into the River Evenlood for over 2 ,600 hours in the last year. Thames Water was allowed by Ofwap to withdraw£7 billion in dividends. Would the Prime Minister agree with my constituents and me that the system is broken? That's Lib Dem MP Callum Miller putting the state of the Thames under the spotlight in Sir Keir Starmer's very first PMQs back in July 2024. The environmental condition of Britain's waterways, and especially the Thames, has always been a concern of the public and successive governments.

3:29Lucy Tobin: Sir Keir had a similar line when the Tories were in charge. After 14 years of failure with our rivers and beaches, it falls to this government of service to fix the mess of the failure of the last 14 years. The government minister responsible at the time promised a big shake-up to how our water is managed and how it's regulated. Such promises keep being made. A once-in-a-generation reform. A water system that delivers safe and secure water supplies, better water quality and a fair deal for customers and indeed for investors. That was in January this year. But what is in the river that everyone is arguing about?

4:11parts of it are healthy, parts of it are unhealthy and many parts of it are somewhere in between. It's impossible to say how healthy it is as a whole. I can take you to places where the river is absolutely beautiful but it just turns into a horrible, horrible mess and people know what they used to see and they know what they see now.

4:30Lucy Tobin: We're joined by campaigners Joe Bradley from Stormwater Shepherds and Ash Smith from Windrush Against Sewage Pollution. Together with industry experts and politicians, to help us work out just how healthy the Thames really is and what we should be doing about it. The first question I'm wondering is, does brown always mean dirty?

4:55We always have a constant challenge of the Thames being brown. And of course, people associate brown with being dirty. So we're always starting off on the back foot. But I mean, that brown is natural, it's healthy. that's got loads of nutrients that make it a rich ecosystem. What we've got to stop doing is categorising the entire river as one thing and recognise that it's made up of many, many parts and then focus on improving the health of those parts.

5:25Lucy Tobin: That's Alison Debney from ZSL and Joe Bradley again. From its estuary in Essex and Kent to Teddington Lock in West London, the Thames is tidal, meaning the river is constantly being churned by the eternal movement of high and low tide. It's that which kicks up sediment from the bottom and makes the river brown. For 9 million Londoners, that's their version of the Thames. But for the millions of other people living in the Thames catchment west of Teddington, the Thames is an altogether different river.

6:02If the river is flowing at its normal rate without any rainfall and so on. The rivers can be quite clean and clear. The further up you go, the clearer it becomes. For the river to be clean, it's really the evidence of that is when there's a thriving wildlife present on the river and that we ourselves are able to use the river for our drinking water.

6:29Lucy Tobin: Chris Finch of the Thames River Society says that the Thames is in a better state today than at its two historic low points. The first was the Great Stink of 1858, which inspired one of the largest Victorian mega-projects, the London sewage system. London sewage was flowing directly into the Thames, and it flowed so slowly back and forth as a tidal river that the effluent of London did not escape the river, and it got more and more polluted, more and more disgusting. Peter Bazalgette, great-great-grandson of Sir Joseph Bazalgette, the engineer behind the scheme. A second nadir in the Thames' lifespan was more recent.

7:11Lucy Tobin: In 1957, the water quality of the tidal Thames was so poor that the river was declared biologically dead. There was so little oxygen in the water that nothing could live it. It couldn't sustain life. So for long stretches of the river, you wouldn't see any fish, for example, living in it. Today, public perception of the River Thames is at a fresh low. Fueled in part by Dirty Business, the Channel 4 docudrama, which follows the investigations of Peter Hammond and Ash Smith. Illegal pollution is profitable. Thames Water is not an exception in adopting that. They've all done it. All the water companies act like this.

7:51they are dumping untreated sewage for months on end. Months.

7:57Lucy Tobin: I put that accusation to Catherine Ross, head of strategy at Thames Water. We do discharge untreated sewage into the river, particularly when there's been high rainfall events or if our assets haven't been working as they should. We monitor that, we report that. Sometimes we are held to account by our regulators for that, if that is appropriate. And we are working extremely hard to improve that position and reduce that level of untreated discharge. There's billions of pounds going in in the next five years to upgrade those serious treatment works and increase their capacity. So I think the idea that we're somehow disregarding river health and behaving in a way that is cavalier for profit is just not borne out by reality.

8:49Lucy Tobin: Most see the body with the greatest responsibility for the river's health as Thames Water. When the company was privatised in 1989, Margaret Thatcher's government wiped its slate clean, meaning it started with zero debt. Since then, a succession of private owners, most notoriously the Australian investment bank Macquarie, which owned Thames Water between 2006 and 2017, used London's water company to generate significant returns for its investors. They practised leveraging, meaning they took out massive loans against the company's assets and paid themselves huge dividends. By the time Macquarie sold up, Thames Water's debt had ballooned to nearly£11 billion.

9:37Lucy Tobin: Almost the same amount had been paid out to its shareholders. Currently, Thames Water is£20 billion in debt. The company didn't borrow to fix the Victorian pipes, but to pay its investors. Today, in 2026, creditors are desperately offering to write off 30 % of Thames Water's debts to avoid losing everything. Meanwhile, customers are being asked to foot the bill to fix the broken network. And the criticism of DEFRA, the Environment Agency and Ofwatt is that they were all asleep at the wheel. That's what Sir Ed Davey, leader of the Liberal Democrats, believes.

10:24If you remember what the public thought about MPs during the expense of scandal, or banks after the crash, you get a sense of what they think about Thames Water. But it's not just the financial management. People are fed up of sewage in their rivers. And the environmental performance of Thames has rightly enraged people. And I share their anger, frankly. So recently, I was going to go kayaking on the Thames in Oxfordshire. I was really looking forward to it. I wasn't intending to fall in that time either. we were going on litter pick you know picking litter run for the banks in the river they had dumped a load of sewage the day before and apparently it happened relatively regularly but they had hoped it wouldn't happen before our event and we were told we couldn't go kayaking people can't just go on the water and do basic things they can't do the things that they expect rightly to be able to do because Thames Water hasn't managed its sewage plants properly You can go to many other countries that manage to do it.

11:29Why can't we?

11:31Lucy Tobin: Critics ask if the regulator is there to protect the river or to protect the balance sheets of the polluters. Are we back to a situation like 1858, the year of the Great Stink? That was when the river outside Parliament was so disgusting that politicians were compelled to give the go-ahead to a hugely expensive new sewer network. I asked Ed whether we're at a similar inflection point today. In PMQs, this debate has come up quite a few times. I was wondering how seriously is it taken in Parliament? Is it, you know, oh, we're debating this again, or is it we can really make a difference? Well, until we take action, like they did after the Grey Stink, it's not been taken seriously enough, has it?

12:14And governments, whether it's ministers in DEFRA or the regulator Ofwat, have failed to blow the whistle. That's one of the reasons why we have said we need a system-wide change. The government have long last looked at it, but I'm not even convinced that they're reorganising the regulators properly. So we're going to keep on with this because Thames needs to get changed seriously. There needs to be way more transparency, but the whole system needs to be changed. In your view, the job of providing clean water and taking away sewage in London is a doable job.

12:47Lucy Tobin: The investment would be available. it's the ineptitude of Thames Water and its previous managers that has caused its problems. 100%. We're a great country. This is a great city. We've got businesses and managers who are more than capable of making this big investment. But I, you know, I have to say I raised an eyebrow about doing this interview. I did it because I think the standard is a great paper and like to support it. It's the paper for the capital. But the fact that Thames Water is sponsoring this did raise an eyebrow. Thames Water seems to have money for lots of things on PR and puffing themselves up.

13:21I'd just like them to do the basics right, please.

13:23Lucy Tobin: In theory, I agree, but I don't think this could be described as puffing it up. I hope not, because I'm certainly not involved in that. I want to hold Thames Water to account, and I think they should be. And I think I speak on behalf of the 60 million customers of Thames Water who are pretty angry with the way they've been treated. And they're angry, frankly, with the politicians who allow this to happen. I asked Thames Water's Catherine Ross whether she believes the company has any responsibility for the health of the river. We have a really important role to play. Not only do we discharge into the River Thames and we affect the aquatic environment there, but we also take a lot of our drinking water out of the River Thames and it's important that the Thames stays healthy for us to do that.

14:08It's also important to recognise that the Thames is an ecosystem And it's a complex system. And although we are called Thames Water and Thames Water is very important for what we do, we're not the only contributor to the health of the River Thames.

14:24Lucy Tobin: So you do believe the Thames Water has a responsibility to look after the health of the River Thames. Would you swim in it? I might. I have done in the past. But I would absolutely check our real-time discharge map to make sure that I wasn't going in after a period of heavy rainfall. And I would recommend that everybody does that if they are thinking about swimming in the river.

14:54Lucy Tobin: If you were standing on the banks of the Thames, boats passing, people walking along the embankment, You wouldn't know it, but tons of poo are flowing just beneath the pavement. A 16-mile super sewer running under London, designed to capture the stormwater and sewage that would otherwise spill into the Thames. Since its opening in 2025, it's been described as a major step forward. And here in central London, it should make a real difference to sewage flowing into the Thames. But it's not a complete solution, because the Thames doesn't begin here. It begins more than 100 miles upstream, in smaller rivers and tributaries that don't have the same level of infrastructure.

15:42Lucy Tobin: And in those places, the problems look very different. Former police detective Ash Smith saw that firsthand. And alongside Oxford data scientist Peter Hammond, he formed a campaign group, Windrush Against Sewage Pollution, or WASP. They focused on the River Windrush, a tributary of the Thames in the Cotswolds, documenting repeated occasions of overflowing sewage over several years. It was quite clear that our rivers were in horrible decline and that the environment agencies seem to have adopted the job of just managing that decline rather than stopping it. Ash believes that the River Thames itself gets off relatively lightly.

16:28The River Thames actually doesn't get hit directly by sewage very often. Mostly the sewage goes into a tributary of the river and that river is often the protective factor so that it does the tertiary treatment, it does some treatment. By the time that water reaches the Thames, it's often better. So I think the Thames is inflated in its quality by the fact that it's protected by a whole load of damaged tributaries.

16:56Lucy Tobin: Sewage isn't just unpleasant, it can be dangerous. As well as bacteria like E. coli, it contains nutrients such as nitrates, which strip oxygen from the water and create so-called dead zones. so when untreated sewage enters the river it doesn't just affect how it looks it changes what can live in it Yet these discharges are regulated and often permitted They're designed to prevent the system from becoming overwhelmed during heavy rainfall Because when stormwater mixes with sewage in London's Victorian pipe network it has to have somewhere to escape Critics argue that what was meant to be an emergency measure has become far more routine.

17:48Lucy Tobin: The system is failing to cope when under pressure. We have this complete fixation on sewage pollution. There are myriad things affecting the health of the river. Agricultural pollution, misconnections of people's washing machines, stormwater runoff from schools and factories and roads and buildings and hospitals and sewage as well and we're completely missing the picture of the overall river health. Joe Bradley from Stormwater Shepherds is going to help me forensically examine what goes into the river in the next episode including that toxic runoff from our roads but for now I'm interested in what we take out of it because as well as trying to manage our sewage Thames water has a statutory duty to deliver safe drinking water to around 10 million Britons.

18:41It's not just about public water supply, that's really important, but it's also about navigational use and it's about the environment and keeping the levels in the Thames high to make sure that we keep all those three aspects working is really important for us.

18:57Lucy Tobin: Neville Moncaster is the Strategic Water Resources director for Thames Water. Stripping away the corporate title, that means his job is to ensure London's water supply doesn't run dry. About 30 % of all water comes from the ground for water supply, 70 % from the river. The main source of water for London is the River Thames. Removing water from the river is called abstraction. Thames Water has to apply for a licence to do this from the Environment Agency roughly every six years. We work very closely with the Environment Agency, for instance, on how we manage the River Thames, how we maintain the right levels in the River Thames and how we manage any water that we take out of it, our abstractions, to ensure that we protect all the facets that we can.

19:43Lucy Tobin: Since the Thames is tidal up to Teddington Lock, the water is salty and therefore undrinkable. So that huge thirsty population living by the tidal, and, remember, brown parts of the Thames, relies on water drawn sometimes miles and miles west of where they live. A complex network of pumping stations, underground pipes and reservoirs keep the water ready for someone to turn on the tap in Turnham Green, say, or switch on the shower in Shoreditch. It's a pumping station that takes water out. They have screens on to make sure they only take water and nothing else and they protect the fish that live in the river.

20:23And then we pump them into the reservoirs, we store and hold the water there until we need it to take to our water treatment works and then treat and pump the water into supply.

20:34Lucy Tobin: Neville sees the majestic Thames a little differently to you or I. To him, a series of weirs along the river change it into a gigantic, cascading water pipe. Because of the number of weirs that you have across the Thames, it actually acts as a series of ponds as water flows from the west to the east, filling each pond and moving on each turn. And whilst you don't really see that as a user of the Thames, when you are trying to manage the water resources of the Thames, it's really important to understand how those ponds fill up and which ponds you're drawing from. London is one of the driest regions in Britain, with approximately 25 % less rain than the national average.

21:17Lucy Tobin: And yet, every day 2.6 billion litres of water are consumed by Thames Water customers. Some of it might even be in that reusable water bottle next to you. But if that flow of cascading ponds are disrupted, then Neville has an inbox of problems. When it's dry, that means that we can take less water out of the river because the levels are lower. And we have to manage that carefully. we're seeing longer, drier summers. I've been working for Thames now for just over four years and I've experienced two droughts already since I've been here. Four of the last summers have been amongst the hottest on record.

21:53Lucy Tobin: Climate change is a huge concern for London's drinking supply. So part of Thames Water's work is to catch and store rainfall for the drier months. Man-made reservoirs do an increasing amount of the heavy lifting, but nature, in the form of giant underground stores called aquifers prevent the Thames from running low. The river flows very much from the spring sources that come out of our limestone aquifers over in the west of the country. Think of a sponge that fills up with water when it rains and then will gradually release that water when it stops raining and that's what provides the source of the Thames, that's where the water comes from and flows down.

22:33Lucy Tobin: Those pretty Cotswold villages in Oxfordshire and Gloucestershire are built using limestone, a honey-coloured sedimentary rock that holds the source of the River Thames, about 80 miles west of London. But those Cotswold aquifers are far from perfect. Aquifers in the west are what we call quite flashy. That means that they fill up quickly, which is great news when it rains because we have lots of water stored, but they also empty quickly. So what we'll see is if you get a drought in the west of the country, the aquifers then start to drain down. And what that means is one of your prime sources of the Thames is starting to dry down and we'll see reduced flows in the Thames.

23:12And that's really important for us to be able to manage because the Thames has many uses.

23:17Lucy Tobin: We're going to look to the future later in the series. But Neville's already trying to work out how he can maintain the current levels of the Thames. That's as climate change, population growth and, yes, of course, AI is going to make an appearance here somewhere. many more data centres all changed London's water usage. We talk about data centres a lot as being a real core to the economy in the future. A lot of them use water. We need to make sure we've got sufficient supplies so we can keep them going as well. We want to make sure that we're resilient for the most extreme events. So we're designing all our infrastructure so we can accommodate a 1 in 500 return period.

23:55That means that the most extreme period will only happen once every 500 years. So we are able to ensure and guarantee people that they'll have water all the time.

24:08Lucy Tobin: So the Thames begins as a small spring in the Cotswolds and ends as a wide tidal river flowing past one of the greatest cities on Earth. And to properly gauge its health, there is no more important marker than assessing its non-human population. we've got really diverse invertebrate life birds seals porpoises you name it and much of that has been down to the real hard work that's that's gone in over the last sort of 50 to 70 years to help the riverway recover from the state it was in in the 1950s we saw much of the Thames being declared as biologically dead you wouldn't find a fish in many of the structures of the tidal Thames Catherine Head is also from the Zoological Society of London a science-driven conservation charity which has a big stake in the health of the Thames and much of its work concentrates on the area from Teddington Lock to the Cotswolds Despite our associations of the Thames being a city river the large majority is actually rural Today just 1 % of the tidal part of the Thames waterway is in its natural state But the river ecology is recovering and in the next episode we'll be looking in more detail at the seals and porpoises that have been spotted in the Thames in recent years.

25:35Lucy Tobin: At the start of the episode I asked a simple question. How healthy is the Thames today? And after everything we've heard, the answer clearly isn't simple. Parts of the river are improving, others are under real pressure. It depends where you look and who you ask. from its fragile limestone at the source to the tidal stretch in central London. This is a river shaped by millions of people and managed by a system that isn't holding up and the responsibility for its health is still being argued over. This is Thames Unfiltered by The Standard in association with Thames Water. Next time on Thames Unfiltered we'll take a closer look at what's actually in the water.

26:24Lucy Tobin: because if we want the Thames to be cleaner we first need to understand what clean really means to a river that's home to myriad species supplying millions of people with drinking water while also being polluted by sewage. This podcast was produced by The Standard and Message Heard in association with Thames Water with all content created under The Standard's editorial control. I'm your host, Lucy Tobin. From The Standard, Tori Frost is our executive producer and Vanessa Cutt is our senior project manager. From Message Heard, Mark Kendrick is our senior producer, Will Aspinall is our producer, Martha Tipper is our assistant producer, Lizzie Andrews and Alan Lear are our audio engineers and James Cox is our production coordinator.