Meghan Hodges
The River Thames and the River Seine have long been used as drains and sources of drinking water, and both have been contaminated by industrialization in the 20th century. In recent years, both have undergone significant transformations in water quality, with the Seine costing nearly a billion pounds to restore. Despite these improvements, both rivers still face significant pollution challenges, with the Thames being considered the cleanest river in the world that flows through a major city.
| Characteristics | Values |
|---|---|
| Pollution in the past | Both the Seine and Thames were considered filthy in the past due to contamination caused by industrialization in the 20th century. |
| Recent improvements | Both rivers have undergone significant transformations in water quality in recent years. |
| Current pollution levels | The Seine still faces significant pollution challenges, including high levels of E. coli and other harmful bacteria during heavy rainfall. |
| The Thames is considered the cleanest river flowing through a major city, with 125 species of fish and over 400 invertebrates. However, raw sewage is still pumped into the river during heavy rains. | |
| Efforts to clean up | Paris has invested around $1.5 billion in a major cleanup project for the Seine, including new infrastructure to reduce pollution from stormwater runoff and combined sewer overflows. |
| London has implemented major infrastructure projects like the Thames Tideway Tunnel to reduce sewage overflows into the river. | |
| Impact of climate change | Climate change may make it harder to clean up rivers like the Seine. |
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What You'll Learn
- The Thames is considered the cleanest river flowing through a major city
- The Seine has improved water quality due to a $1.5 billion cleanup project
- The Thames Tideway Tunnel has reduced sewage overflow into the river
- The Seine's pollution is exacerbated by heavy rainfall
- The Thames was an open sewer until the 19th century
The Thames is considered the cleanest river flowing through a major city
The clean-up of the Thames is an ongoing process, with major infrastructure projects like the Thames Tideway Tunnel significantly reducing sewage overflow into the river. Despite these improvements, raw sewage is still pumped into the river during heavy rains.
The Thames' transformation has inspired hopes of replicating its success in other cities. Paris, for example, has embarked on an ambitious journey to clean up the Seine River before the 2024 Olympic Games. The Seine, like the Thames, suffered contamination due to industrialization in the 20th century. A $1.5 billion cleanup project aims to make the river swimmable again, addressing issues such as stormwater runoff and combined sewer overflows.
While the Seine's water quality has improved, it still faces significant pollution challenges. During heavy rainfall, combined sewer overflows can introduce harmful contaminants, including E. coli bacteria. The presence of these bacteria complicates water quality management and poses health risks.
The efforts to restore the Seine and the Thames highlight a broader trend of addressing water pollution in urban areas. With dedicated initiatives and infrastructure developments, cities are working towards revitalizing their waterways and ensuring the protection and restoration of degraded ecosystems.
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The Seine has improved water quality due to a $1.5 billion cleanup project
The Seine and the Thames were both heavely polluted due to industrialisation in the 20th century. However, the Seine has seen a significant improvement in water quality due to a $1.5 billion cleanup project, with the aim of making the river swimmable again for the 2024 Paris Olympics. This project has involved developing new infrastructure to reduce pollution from stormwater runoff and combined sewer overflows. The construction of a giant rainwater runoff tank helps to prevent the sewer system from overflowing and subsequently stops discharges of sewage into the river.
The cleanup project has sparked optimism for the improvement of other polluted rivers, with Dianna Kopansky, Head of the Freshwater and Wetlands Unit of the United Nations Environment Programme (UNEP), stating:
> "Paris has shown that it is possible to bring even the most polluted rivers back to life. But if we’re to ward off a looming freshwater crisis, the world is going to need a lot more success stories like this."
Despite these improvements, the Seine still faces challenges with pollution. During heavy rainfall, combined sewer overflows can introduce harmful bacteria such as E. coli into the river, which poses a significant health risk. Nevertheless, the cleanup efforts have been largely successful, with the river deemed safe for swimming during the Olympics and Paralympics.
The Thames has also seen dramatic improvements in water quality since the mid-20th century, with major infrastructure projects helping to reduce sewage overflows. The river is now considered the cleanest in the world flowing through a major city, with 125 species of fish and over 400 invertebrates calling it home. However, raw sewage is still pumped into the river during heavy rains, highlighting the ongoing need for better water management and infrastructure.
The cleanup efforts of the Seine and the Thames provide a glimmer of hope for other polluted rivers worldwide, demonstrating that it is possible to restore even the most degraded waterways.
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The Thames Tideway Tunnel has reduced sewage overflow into the river
The Thames and the Seine have long been regarded as filthy, contaminated by industrialization in the 20th century. However, both rivers have seen significant improvements in water quality in recent years. The Seine, in particular, has undergone a major cleanup project in preparation for the 2024 Paris Olympics, aiming to make the river swimmable again. Despite these improvements, the Seine still faces pollution challenges, especially during heavy rainfall when combined sewer overflows can introduce harmful bacteria like E. coli.
Similarly, the Thames has also faced issues with sewage overflow, particularly in London where older inner boroughs have combined sewerage systems that cannot handle the city's growth. To address this, the Thames Tideway Tunnel, a deep-level sewer, was constructed along the tidal section of the River Thames. This 16-mile tunnel runs from Acton in the west to Abbey Mills in the east, where it connects to the Beckton Sewage Treatment Works. The tunnel captures raw sewage and rainwater that would otherwise overflow into the river during heavy rain, storing it until it can be treated.
The Thames Tideway Tunnel project, also known as the London Tideway Improvements, consisted of three parts. The first was the Lee Tunnel, a 6.9-km tunnel that captures sewage from London's most polluting CSOs and conveys it to the Beckton Sewage Treatment Works. The second part involved modernizing and extending London's five major sewage treatment works to increase their capacity and reduce the need for stormwater tanks.
The final part was the Thames Tideway Tunnel itself, which intercepts outflows from polluting CSOs, stores them, and conveys them for processing. This tunnel is designed to capture almost all the raw sewage and rainwater from combined sewers, preventing them from overflowing into the river. The project cost £4.2-5 billion and is funded by Thames Water customers, causing some controversy. The tunnel officially opened in May 2025, with the last of the 21 connections completed in February of that year.
In conclusion, the Thames Tideway Tunnel has been a significant step in reducing sewage overflow into the Thames River, addressing a long-standing issue in London. By capturing and storing sewage and rainwater, the tunnel prevents overflow into the river during heavy rain, improving water quality. This project, along with similar improvements to the Seine, gives hope that even the most polluted urban waterways can be brought back to life.
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The Seine's pollution is exacerbated by heavy rainfall
The Seine and the Thames, widely regarded as filthy in the past, have both undergone significant transformations in their water quality over recent years. However, the Seine's pollution is still exacerbated by heavy rainfall.
During heavy rainfall events, combined sewer overflows can introduce high levels of contaminants to the Seine, including E. coli and other harmful bacteria. While rainwater may dilute planktonic E. coli levels, comprehensive E. coli counts, including bacteria clumped onto faecal or sediment particles, often remain high. These aggregated bacteria pose a more severe health risk and complicate water quality management.
To address this issue, Paris has implemented a giant rainwater runoff tank as part of its efforts to improve water quality in preparation for the 2024 Olympic Games. The tank holds extra water during heavy rainfall, preventing the sewer system from overflowing and discharging sewage into the river. However, despite these measures, pollution levels remained too high for triathletes to compete in the originally scheduled events during the 2024 Olympics opening ceremony, which was affected by rain.
The Thames has faced similar challenges, and major infrastructure projects like the Thames Tideway Tunnel have been implemented to reduce sewage overflows. Additionally, the UK government is constructing the Thames Tideway Scheme at a cost of £4.2 billion to reduce stormwater discharge, although an estimated two million tonnes of sewage are still expected to be dumped into the Thames yearly.
While both rivers have experienced improvements, heavy rainfall continues to impact the Seine's water quality, and more comprehensive solutions are needed to address the issue effectively.
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The Thames was an open sewer until the 19th century
The Thames and the Seine have both been widely regarded as filthy in the past. However, both rivers have undergone significant transformations in their water quality over the years. The Thames, in particular, has come a long way since it was an open sewer until the 19th century.
In the 19th century, London's population numbered around 2 million people. The city suffered fatal epidemics of cholera, which claimed thousands of lives. At the time, it was widely believed that contaminated air, or "miasma", was the vector of transmission for cholera. However, London-based physician Dr John Snow put forward the theory that cholera was a waterborne disease.
The Great Stink of 1858 served as a catalyst for change. The stench from the Thames was so bad that members of parliament in the Houses of Parliament adjourned proceedings. Soon after, parliament sanctioned a new sewer network for London, with Sir Joseph Bazalgette as the mastermind behind the project. Before Bazalgette's designs, raw sewage seeped from inadequate sewers into the Thames, turning it into a stinking open sewer. The new sewage network's enclosed design, which captured sewage and rainwater, virtually eliminated cholera.
In the 1880s, further health concerns led to the purification of sewage at Crossness and Beckton, rather than dumping untreated waste into the river. The sewers were expanded in the late 19th century and again in the early 20th century.
Today, the Thames is considered the cleanest river in the world that flows through a major city. It is home to 125 species of fish and more than 400 invertebrates. However, it still faces challenges, as raw sewage is routinely pumped into the river during heavy rains. Thames Water has proposed building a new sewer to address this issue.
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Frequently asked questions
The Thames is considered the cleanest river in the world that flows through a major city, with over 125 species of fish and more than 400 invertebrates. However, the Seine has undergone a significant transformation in water quality, with the river now deemed suitable for swimming.
No, the Thames was once an open sewer. In 1858, a hot summer resulted in the Great Stink, where centuries of waste in the Thames began to ferment.
Major infrastructure projects like the Thames Tideway Tunnel and Scheme have been implemented to significantly reduce sewage overflows into the river.
The Seine was banned for swimming in 1923 due to high levels of pollution, including E. coli and overflowing sewers.
A major cleanup project costing around $1.5 billion has aimed to make the river swimmable again. New infrastructure has been developed to reduce pollution from stormwater runoff and combined sewer overflows.
