POLLUTION AND CLIMATE CHANGE THREATEN GOOD HEALTH OF RIVER THAMES
THE RIVER THAMES is ringing in 2026 with a new lease of life, according to results from the latest health check of the famous river that was once declared ‘biologically dead’ – although experts warn that issues such as rising water temperatures and pollution threaten this ‘hard-won resurrection’ according to the report.
Published today (19 January 2026) the updated State of the River Thames report by conservation charity ZSL (Zoological Society of London) highlights how decades of dedicated action have bettered the Thames for people and nature – including beloved species such as harbour porpoises and wading birds.
These improvements include lower concentrations of toxic metals, more ‘breathable’ water for the river’s underwater wildlife, and new riverside walkways and nature habitats along its banks that are enjoyed by London’s residents and visitors.
The report also shows how rapidly regulation can bring benefits; plastic cotton bud sticks, once one of the most commonly found litter items in the Thames, have all but disappeared from its shores following the UK’s sale-ban in 2022. ZSL’s conservationists hope the same will be achieved for plastic wet wipes, another disastrous form of pollution found along the Thames, which are due to be banned in the UK later this year.
However, the report also highlights the need for cross-government action to protect the Thames and the essential services that it provides to the nine million people living along it – which include providing drinking water, food, livelihoods, protection from coastal flooding, and offsetting the damaging impacts of carbon emissions.
Conservationist Alison Debney, ZSL Lead for UK Nature Recovery said: “The River Thames isn’t just a famous landmark flowing through the heart of the UK’s capital – it’s a lifeline for all who live along it.
“Every fragment of the Thames put under strain reduces the river’s resilience and threatens the vital services it provides British wildlife and the millions of people living alongside it – whether that’s providing nursery grounds for fish, securing clean drinking water, or providing an outdoor space to enjoy weekends with friends and family.
“As we enter a new year, the Thames reminds us that transformation is possible. The Thames may have been declared ‘biologically dead’ in the 1950s, but the estuary we see today demonstrates just how quickly things can change when decisive action is taken. We’re celebrating those wins today – but we must act now to secure the wins of tomorrow.”
From toxic ‘forever chemicals’ to rising temperatures and sea-levels, the data shows that climate change and pollution – from sources including road run-off, sewage and pharmaceuticals – are putting the estuary in a fragile position.
The summer temperature of the capital’s waterway has increased on average by 0.13⁰C each year since 2007, equivalent to a 1⁰ C temperature rise every eight years.
In the heart of the city, water levels by Tower Bridge and the Tower of London have also been rising – by 5mm each year on average since 1993. As water levels continue to rise, so does the risk of upstream waters becoming increasingly more saline – leading to the loss of rare freshwater tidal habitat along the Thames and the interwoven communities of wildlife that it supports.
Concentrations of nitrates, which are harmful in high amounts, have also gradually increased in the Thames and two of its monitored tributaries – the Rivers Lee and Darent – all of which risks further unbalancing the delicate ecosystem and threatening the important services it provides.
Marking the start of ZSL’s 200th anniversary year, today’s report is an update to the first The State of the Thames published in 2021.
Bringing together the expertise of 21 organisations working across the Thames, the report collates the most up-to-date monitoring data available from 21 different indicators used to assess the health of the Thames – providing conservationists, policy makers and industry leaders with an essential overview of the progress made so far to recover the iconic river.
Other wins for public health and the environment include the drop in concentrations of toxic copper and zinc in the Thames to below levels at which they damage the aquatic ecosystem. Zinc concentrations in 2024 were half the concentrations of 1990, while copper concentrations are only a quarter of that in 1990.
Additionally, while nitrate levels have steadily increased over the last 35 years, the concentrations of another monitored nutrient, phosphorous, have decreased since 1970.
As excess levels of these nutrients can lead to the overgrowth of algae that deplete the river of essential oxygen, this finding marks another win for the Thames – in part due to the upgrade of five London sewage treatment works and investment in the Lee Tunnel.
Both nitrate and phosphorous are found naturally in rivers, but are also associated with sewage, industrial waste and agricultural run-off – underscoring the importance and impact of investment and changes in land management in addressing these issues.
The upgrades were followed by a £4.6 billion investment in The Thames Tideway Tunnel, which was fully connected to the Thames Water network in 2025.
The ‘super-sewer’, along with the Lee Tunnel and treatment works upgrades, are expected to help capture 95% of the volume of untreated sewage currently entering the tidal Thames in a typical year. Since autumn 2024, the tunnels have captured almost 13 million tonnes of sewage that would have been otherwise discharged into the Thames.
The Mayor of London, Sadiq Khan said: “The Thames is London’s lifeblood. It was the cause of London’s founding and remains a working river, a haven for wildlife and a source of joy and wellbeing for millions of Londoners.
“This report shows the progress that has been made, but also just how much more we must do to protect it from pollution and the climate crisis.
“We have made incredible progress cleaning up London’s air in recent years and I’m determined that we do the same with our rivers as we continue to build a greener London for everyone.”
Alison added: “Protecting, reconnecting and restoring habitats across the Thames is key to building a resilient future for people and wildlife alike.”
As part of the conservation charity’s commitment to recovering the famous waterway, 2025 saw the launch of Transforming the Thames, an ambitious, ZSL-led partnership uniting conservationists, communities, government bodies and landowners to scale up recovery across the Greater Thames Estuary.
Plans include the creation of oyster reefs, the planting of seagrass meadows, and restoration of saltmarshes that provide critical nesting grounds for local bird populations.
Charlie Wood, London Area Director at the Environment Agency said: “This ZSL report is a brilliant spotlight on the health of the River Thames and we are delighted to have contributed. It is through such monitoring and evidence that we can understand the progress Thames health check celebrates rebirth of famous river Conservationists usher in New Year celebrating wins for iconic river, and outline next steps for further recovery as they publish landmark report
THE THAMES is ringing in 2026 with a new lease of life, according to results from the latest health check of the famous river that was once declared ‘biologically dead’ – although experts warn that rising water temperatures and pollution threaten this hard-won resurrection.
Published today (19 January 2026) the updated State of the River Thames report by conservation charity ZSL (Zoological Society of London) highlights how decades of dedicated action have bettered the Thames for people and nature – including beloved species such as harbour porpoises and wading birds. These improvements include lower concentrations of toxic metals, more ‘breathable’ water for the river’s underwater wildlife, and new riverside walkways and nature habitats along its banks that are enjoyed by London’s residents and visitors.
The report also shows how rapidly regulation can bring benefits; plastic cotton bud sticks, once one of the most commonly found litter items in the Thames, have all but disappeared from its shores following the UK’s sale-ban in 2022. ZSL’s conservationists hope the same will be achieved for plastic wet wipes, another disastrous form of pollution found along the Thames, which are due to be banned in the UK later this year.
However, the report also highlights the need for cross-government action to protect the Thames and the essential services that it provides to the nine million people living along it – which include providing drinking water, food, livelihoods, protection from coastal flooding, and offsetting the damaging impacts of carbon emissions.
Conservationist Alison Debney, ZSL Lead for UK Nature Recovery said: “The River Thames isn’t just a famous landmark flowing through the heart of the UK’s capital – it’s a lifeline for all who live along it. Every fragment of the Thames put under strain reduces the river’s resilience and threatens the vital services it provides British wildlife and the millions of people living alongside it – whether that’s providing nursery grounds for fish, securing clean drinking water, or providing an outdoor space to enjoy weekends with friends and family.
“As we enter a new year, the Thames reminds us that transformation is possible. The Thames may have been declared ‘biologically dead’ in the 1950s, but the estuary we see today demonstrates just how quickly things can change when decisive action is taken. We’re celebrating those wins today – but we must act now to secure the wins of tomorrow.”
From toxic ‘forever chemicals’ to rising temperatures and sea-levels, the data shows that climate change and pollution – from sources including road run-off, sewage and pharmaceuticals – are putting the estuary in a fragile position.
The summer temperature of the capital’s waterway has increased on average by 0.13⁰C each year since 2007, equivalent to a 1⁰ C temperature rise every eight years. In the heart of the city, water levels by Tower Bridge and the Tower of London have also been rising – by 5mm each year on average since 1993. As water levels continue to rise, so does the risk of upstream waters becoming increasingly more saline – leading to the loss of rare freshwater tidal habitat along the Thames and the interwoven communities of wildlife that it supports.
Concentrations of nitrates, which are harmful in high amounts, have also gradually increased in the Thames and two of its monitored tributaries – the Rivers Lee and Darent – all of which risks further unbalancing the delicate ecosystem and threatening the important services it provides.
Marking the start of ZSL’s 200th anniversary year, today’s report is an update to the first The State of the Thames published in 2021. Bringing together the expertise of 21 organisations working across the Thames, the report collates the most up-to-date monitoring data available from 21 different indicators used to assess the health of the Thames – providing conservationists, policy makers and industry leaders with an essential overview of the progress made so far to recover the iconic river.
Other wins for public health and the environment include the drop in concentrations of toxic copper and zinc in the Thames to below levels at which they damage the aquatic ecosystem. Zinc concentrations in 2024 were half the concentrations of 1990, while copper concentrations are only a quarter of that in 1990.
Additionally, while nitrate levels have steadily increased over the last 35 years, the concentrations of another monitored nutrient, phosphorous, have decreased since 1970. As excess levels of these nutrients can lead to the overgrowth of algae that deplete the river of essential oxygen, this finding marks another win for the Thames – in part due to the upgrade of five London sewage treatment works and investment in the Lee Tunnel.
Both nitrate and phosphorous are found naturally in rivers, but are also associated with sewage, industrial waste and agricultural run-off – underscoring the importance and impact of investment and changes in land management in addressing these issues.
The upgrades were followed by a £4.6 billion investment in The Thames Tideway Tunnel, which was fully connected to the Thames Water network in 2025. The ‘super-sewer’, along with the Lee Tunnel and treatment works upgrades, are expected to help capture 95% of the volume of untreated sewage currently entering the tidal Thames in a typical year. Since autumn 2024, the tunnels have captured almost 13 million tonnes of sewage that would have been otherwise discharged into the Thames.
The Mayor of London, Sadiq Khan said: “The Thames is London’s lifeblood. It was the cause of London’s founding and remains a working river, a haven for wildlife and a source of joy and wellbeing for millions of Londoners.
“This report shows the progress that has been made, but also just how much more we must do to protect it from pollution and the climate crisis.
“We have made incredible progress cleaning up London’s air in recent years and I’m determined that we do the same with our rivers as we continue to build a greener London for everyone.”
Alison added: “Protecting, reconnecting and restoring habitats across the Thames is key to building a resilient future for people and wildlife alike.”
As part of the conservation charity’s commitment to recovering the famous waterway, 2025 saw the launch of Transforming the Thames, an ambitious, ZSL-led partnership uniting conservationists, communities, government bodies and landowners to scale up recovery across the Greater Thames Estuary. Plans include the creation of oyster reefs, the planting of seagrass meadows, and restoration of saltmarshes that provide critical nesting grounds for local bird populations.
Charlie Wood, London Area Director at the Environment Agency said: “This ZSL report is a brilliant spotlight on the health of the River Thames and we are delighted to have contributed. It is through such monitoring and evidence that we can understand the progress made to bring the river back to a thriving state but also identify emerging threats from factors such as climate change.
“Strong regulation and steering investment in infrastructure has played a major role in the improvements we see, but the future of the Thames also relies on working in partnership across the public, private and voluntary sectors and we look forward to continuing our role in that.”
ZSL believes nature can recover, and that conservation is most effective when driven by science. Find out more and support ZSL’s world-leading, collaborative science and conservation work at www.zsl.org
Stuart Higgins
– ENDS –
EDITORS’ NOTES