Once Deemed ‘Biologically Dead,’ a New Report Shows London’s River Thames Recovering

Though wildlife populations are recovering, climate change and sewage still threaten the river’s health

Two seals lay on the riverbank. The blue water flows in front of them, and they rest on a sandy patch near some grass.
Species like seals, sharks, seahorses and eels have found their way back to the river in recent decades. Zoological Society of London

The 215-mile-long River Thames cuts through southern England, flows through London and opens at the English Channel. As London's population grew over the course of centuries, so did its impact on the river. By 1957, scientists at the Natural History Museum of London declared large swaths of the Thames to be so polluted that they were "biologically dead."

To gauge the health of the river, a team of scientists conducted a variety of tests, and they published the results in the first-ever State of the Thames Report this week. In optimistic news, they found that the river is once again home to species such as sharks, eels, seals and seahorses, reports the BBC.

"This report has enabled us to really look at how far the Thames has come on its journey to recovery since it was declared biologically dead, and in some cases, set baselines to build from in the future," Alison Debney, a leader of the Zoological Society of London's conservation program, says in a press release.

Populations of birds and marine mammals have positive short-term and long-term projections, and many long-gone species have returned to the river. For example, around 20 years ago, little was known about seals living in the river, but the report highlights the abundance and location of two species: the harbor and gray seal, reports Scott Neuman for NPR.

The team documented 115 fish species in the river, but the number of species has declined since the early 1990s. The cause of this decline is still unknown, according to the press release.

However, the report also highlighted major concerns due to climate change, such as rising temperatures and sea levels. Some stretches of the river have warmed by 0.34 degrees Fahrenheit annually since 2007, threatening the delicate ecosystem, reports Amy Cheng for the Washington Post.

Though sewage treatment and the flow of waste into the river has dramatically improved in recent decades, the problem isn't solved yet. As a result, the report shows an increase in nitrates, which negatively affect water quality and wildlife. The Environmental Agency deemed that the increased nitrates come from industrial waste and sewage flowing into the water around London, according to the press release.

"Because London's sewage system was largely built in the 1800s when London's population was less than a quarter of what it is today, storm events cause excess sewage to overflow into the Tidal Thames, posing a major threat to water quality," the report says.

As a solution, London is working on the Thames Tideway Tunnel, which will collect and store raw sewage instead of allowing it to overflow into the tidal basin, NPR reports.

"This report comes at a critical time and highlights the urgent need for the Thames Tideway Tunnel, known as London’s new super sewer," Liz Wood-Griffiths, a project leader for the tunnel, says in the press release. "The new sewer, which is due to be complete in 2025, is designed to capture more than 95 per cent of the sewage spills that enter the River from London’s Victorian sewer system. It will have a significant impact on the water quality, making it a much healthier environment for wildlife to survive and flourish.” 

In the meantime, the Zoological Society of London is partnering up with conservationists and other groups to restore parts of the river with native seagrasses and critters like oysters.

"Between them, these not only help to restore wildlife in the river, but also act as natural flood defenses, and help to mitigate against extreme weather such as storms and floods," Debney says in the press release. "A resilient future for both people and wildlife will depend on protecting remaining natural habitats, reconnecting and restoring habitats, and innovating new ways to maximize opportunities for wildlife in the urban environment."

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