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 on Monday (19 January), the report updated The State of the Thames report by conservation charity ZSL's team and highlights how decades of dedicated action have bettered the Thames for people and nature – including beloved species such as harbour porpoises and wading birds.

ZSL said: "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. 

The charity added: "We 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's 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.

"Protecting, reconnecting and restoring habitats across the Thames is key to building a resilient future for people and wildlife alike."

She added: "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."

Marking the start of ZSL's 200th anniversary year, Monday's report is an update to the first The State of the Thames report, 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. 

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." 

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.

ZSL said: "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." 

Charlie Wood, London Area Director at the Environment Agency added: "This ZSL report is a brilliant spotlight on the health of the River Thames and we are delighted to have contributed.

"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."