The Thames is a rare urban success story, but there are three clouds on the horizon

Wander down to the foreshore of the Thames or to the solid embankment in the heart of the city and the river may look a little brown but is clearly well used by birds and perhaps you might catch a glimpse of one of the river’s 3,500 seals. Four years ago, an Orca whale became trapped in a lock.

Yet almost 70 years ago the River Thames was declared biologically dead as decades of pollution poured into the water by the industries that had grown up by its banks and upstream on its tributaries made it unliveable for the scores of fish and mammals it used to host.

It’s now full of wildlife thanks to improvements in sewage and industrial waste treatment. More than 120 species of fish have been recorded in the river since the late 1950s and marine mammals such as those seals and even porpoises have made a remarkable recovery.

Sealing the deal: two sunbathing mammals. Photo by Miquel Parera on Unsplash

But the story of an urban river reborn faces threats from three challenges, which all share their origins in the ongoing human-induced changes to our climate.

The first challenge comes from the slow but unremitting impact of a changing climate on the river’s ecosystem especially as it approaches the English Channel. As ZSL, the conservation charity best known for managing London‘s zoo, points out, the Thames Estuary has lost substantial coastal habitats, reducing its ecological resilience. The remaining fragmented areas are now less capable of regenerating or withstanding environmental challenges.

This habitat degradation limits the estuary's potential ecosystem services, particularly its ability to mitigate climate change impacts.

ZSL says it will have the habitat restoration plan completed by next month (March 2025) and hopes to embark on the first five years of delivery from later that year. However, the habitat restoration plan will consider a much longer timeframe beyond the first five years, with consideration of projects that could be delivered up to 2055.

Thames21, an independent charity that emerged from a partnership of some 25 public and private bodies, has launched a five-year programme lasting until 2028 to offset the way that climate change has intensified extreme weather patterns. Escalating incidents of intense heat, water scarcity, and significant precipitation are increasing the susceptibility of London and Thames Basin regions to environmental risks.

Swimming against the flow

An associated challenge is the pressures that humans put on the river that can exacerbate those problems. In the 19th and first half of the 20th century that was pollution; the more modern version is the increased need for buildings to add business and residential accommodation and to speed up journeys.

The redevelopment of the London Docklands has seen apartment blocks spring up around the Isle of Dogs and on the Greenwich shores, matched by a line of high-rise developments along the south bank of the Thames from Vauxhall to Battersea Power Station.

The recent decision to move forward with the Lower Thames Crossing has been met with dismay for supports of the river’s ecosystem. The government justifies the decision saying that it is needed to offset excess demand for the Dartford Crossing, doubling capacity and reducing journey times. Opponents says that it will damage eight hectares of ancient forest, generate 6.5 million tonnes of CO2 — making it UK's most carbon-intensive road project) — and degrade local air quality.

A leisure facility: but is the water clean? Photo by Harry Grout on Unsplash

The third threat comes from growing pharmaceutical pollution in the Thames. Scientists have recently identified an increase in ingress of sewage containing pharmaceutical products and recreational drugs. These can have negative impacts on the environment, public health and aquatic organisms such as fish, invertebrates and plants as well as on humans.

Research has shown they are now omnipresent in the Thames: a 2016 study along the 215 miles from the source in Kemble, Gloucestershire, to the North Sea detected 44 pharmaceuticals and two lifestyle compounds (cocaine and sucralose). The release of micro-organic compounds is seen as raising the risk of negative impacts. While the effects of some drugs are reduced through time and sewage processing, some have been found to be harmful. For example, anti-inflammatory drugs such as diclofenac can harm fish as well as predatory birds through secondary poisoning.

The primary focus for a coordinated response will be the completion of the Thames Tideway “super sewer” system that is forecast to reduce discharges by 93% compared with 2015. However, that will leave an estimated 2.5 million tonnes flowing into the Thames annually. Other options are nature-based solutions to complement the engineered investments such as flood management techniques and ponds, the potential for giving legal backing to a “right to rivers”, and investment in greater communication and collaboration in medical prescriptions.

Message in a bottle

The near-death of the River Thames in 1957 was a classic example of unsustainable behaviour flowing through to its ultimate conclusion. The fact that it has been reversed effectively is good news. But it is also a reminder that sustainability must be constantly maintained, as a fallback in standards or attitudes can swiftly lead to bad outcomes that can reinforce each other and multiply, fuelling a negative cycle. The clear message is that all of us — residents, pressure groups, businesses, and investors — must urgently collaborate to safeguard our communities, ecosystems, and critical economic zones from the escalating climate crisis.